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 $116.30   10.433%   $128.4336   $128.43   $128.45   $128.40  
  Purchase #2 $217.33   6.294%   $231.0088   $231.01   $231.00   $231.00  
  Purchase #3 $5.53   13.788%   $6.2925   $6.29   $6.30   $6.30  
  Purchase #4 $218.86   6.809%   $233.7622   $233.76   $233.75   $233.80  
  Purchase #5 $240.46   9.666%   $263.7029   $263.70   $263.70   $263.70  
  Purchase #6 $237.34   12.823%   $267.7741   $267.77   $267.75   $267.80  
  Purchase #7 $16.41   10.655%   $18.1585   $18.16   $18.15   $18.20  
  7 purchase totals = $1,052.23       $1,149.1326   $1,149.12   $1,149.10   $1,149.20