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 $63.66   6.310%   $67.6769   $67.68   $67.70   $67.70  
  Purchase #2 $37.72   9.652%   $41.3607   $41.36   $41.35   $41.40  
  Purchase #3 $46.91   7.507%   $50.4315   $50.43   $50.45   $50.40  
  Purchase #4 $215.38   5.190%   $226.5582   $226.56   $226.55   $226.60  
  Purchase #5 $97.58   5.113%   $102.5693   $102.57   $102.55   $102.60  
  Purchase #6 $94.97   7.634%   $102.22   $102.22   $102.20   $102.20  
  Purchase #7 $145.82   7.142%   $156.2345   $156.23   $156.25   $156.20  
  7 purchase totals = $702.04       $747.0511   $747.05   $747.05   $747.10