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 $129.53   9.168%   $141.4053   $141.41   $141.40   $141.40  
  Purchase #2 $8.54   3.228%   $8.8157   $8.82   $8.80   $8.80  
  Purchase #3 $46.53   5.354%   $49.0212   $49.02   $49.00   $49.00  
  Purchase #4 $59.86   12.473%   $67.3263   $67.33   $67.35   $67.30  
  Purchase #5 $223.43   6.419%   $237.772   $237.77   $237.75   $237.80  
  Purchase #6 $90.50   4.158%   $94.263   $94.26   $94.25   $94.30  
  Purchase #7 $141.44   4.602%   $147.9491   $147.95   $147.95   $147.90  
  7 purchase totals = $699.83       $746.5526   $746.56   $746.50   $746.50