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 $177.32   7.298%   $190.2608   $190.26   $190.25   $190.30  
  Purchase #2 $219.95   10.620%   $243.3087   $243.31   $243.30   $243.30  
  Purchase #3 $54.43   4.692%   $56.9839   $56.98   $57.00   $57.00  
  Purchase #4 $73.54   9.183%   $80.2932   $80.29   $80.30   $80.30  
  Purchase #5 $13.40   6.312%   $14.2458   $14.25   $14.25   $14.20  
  Purchase #6 $247.97   7.467%   $266.4859   $266.49   $266.50   $266.50  
  Purchase #7 $76.93   3.607%   $79.7049   $79.70   $79.70   $79.70  
  7 purchase totals = $863.54       $931.2832   $931.28   $931.30   $931.30