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 $133.95   13.433%   $151.9435   $151.94   $151.95   $151.90  
  Purchase #2 $5.43   10.853%   $6.0193   $6.02   $6.00   $6.00  
  Purchase #3 $26.96   9.684%   $29.5708   $29.57   $29.55   $29.60  
  Purchase #4 $228.39   3.715%   $236.8747   $236.87   $236.85   $236.90  
  Purchase #5 $181.87   4.625%   $190.2815   $190.28   $190.30   $190.30  
  Purchase #6 $178.96   7.115%   $191.693   $191.69   $191.70   $191.70  
  Purchase #7 $70.80   4.742%   $74.1573   $74.16   $74.15   $74.20  
  7 purchase totals = $826.36       $880.5401   $880.53   $880.50   $880.60