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 $212.33   13.120%   $240.1877   $240.19   $240.20   $240.20  
  Purchase #2 $58.26   5.157%   $61.2645   $61.26   $61.25   $61.30  
  Purchase #3 $22.30   12.825%   $25.16   $25.16   $25.15   $25.20  
  Purchase #4 $79.56   5.673%   $84.0734   $84.07   $84.05   $84.10  
  Purchase #5 $60.93   4.380%   $63.5987   $63.60   $63.60   $63.60  
  Purchase #6 $49.31   12.353%   $55.4013   $55.40   $55.40   $55.40  
  Purchase #7 $87.28   8.857%   $95.0104   $95.01   $95.00   $95.00  
  7 purchase totals = $569.97       $624.6960   $624.69   $624.65   $624.80