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 $77.41   9.394%   $84.6819   $84.68   $84.70   $84.70  
  Purchase #2 $113.54   5.605%   $119.9039   $119.90   $119.90   $119.90  
  Purchase #3 $48.37   8.407%   $52.4365   $52.44   $52.45   $52.40  
  Purchase #4 $231.51   4.488%   $241.9002   $241.90   $241.90   $241.90  
  Purchase #5 $87.64   10.345%   $96.7064   $96.71   $96.70   $96.70  
  Purchase #6 $211.55   6.265%   $224.8036   $224.80   $224.80   $224.80  
  Purchase #7 $99.89   13.449%   $113.3242   $113.32   $113.30   $113.30  
  7 purchase totals = $869.91       $933.7567   $933.75   $933.75   $933.70