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 $109.93   8.384%   $119.1465   $119.15   $119.15   $119.10  
  Purchase #2 $41.35   7.486%   $44.4455   $44.45   $44.45   $44.40  
  Purchase #3 $183.38   11.186%   $203.8929   $203.89   $203.90   $203.90  
  Purchase #4 $19.35   7.380%   $20.778   $20.78   $20.80   $20.80  
  Purchase #5 $173.41   6.427%   $184.5551   $184.56   $184.55   $184.60  
  Purchase #6 $12.99   9.431%   $14.2151   $14.22   $14.20   $14.20  
  Purchase #7 $22.51   11.135%   $25.0165   $25.02   $25.00   $25.00  
  7 purchase totals = $562.92       $612.0496   $612.07   $612.05   $612.00