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 $53.72   13.594%   $61.0227   $61.02   $61.00   $61.00  
  Purchase #2 $150.34   4.550%   $157.1805   $157.18   $157.20   $157.20  
  Purchase #3 $88.73   7.460%   $95.3493   $95.35   $95.35   $95.30  
  Purchase #4 $38.43   8.459%   $41.6808   $41.68   $41.70   $41.70  
  Purchase #5 $228.41   3.640%   $236.7241   $236.72   $236.70   $236.70  
  Purchase #6 $117.25   6.496%   $124.8666   $124.87   $124.85   $124.90  
  Purchase #7 $183.72   9.275%   $200.76   $200.76   $200.75   $200.80  
  7 purchase totals = $860.60       $917.5840   $917.58   $917.55   $917.60