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 $188.95   9.713%   $207.3027   $207.30   $207.30   $207.30  
  Purchase #2 $160.29   11.280%   $178.3707   $178.37   $178.35   $178.40  
  Purchase #3 $239.76   13.437%   $271.9766   $271.98   $272.00   $272.00  
  Purchase #4 $246.83   12.438%   $277.5307   $277.53   $277.55   $277.50  
  Purchase #5 $137.48   13.494%   $156.0316   $156.03   $156.05   $156.00  
  Purchase #6 $12.36   7.497%   $13.2866   $13.29   $13.30   $13.30  
  Purchase #7 $143.80   4.470%   $150.2279   $150.23   $150.25   $150.20  
  7 purchase totals = $1,129.47       $1,254.7268   $1,254.73   $1,254.80   $1,254.70