Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $178.26   6.178%   $189.2729   $189.27   $189.25   $189.30  
  Purchase #2 $204.75   3.858%   $212.6493   $212.65   $212.65   $212.60  
  Purchase #3 $227.85   9.411%   $249.293   $249.29   $249.30   $249.30  
  Purchase #4 $226.43   13.554%   $257.1203   $257.12   $257.10   $257.10  
  Purchase #5 $240.47   9.400%   $263.0742   $263.07   $263.05   $263.10  
  Purchase #6 $245.51   7.413%   $263.7097   $263.71   $263.70   $263.70  
  Purchase #7 $214.27   13.542%   $243.2864   $243.29   $243.30   $243.30  
  7 purchase totals = $1,537.54       $1,678.4058   $1,678.40   $1,678.35   $1,678.40