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 $49.40   11.730%   $55.1946   $55.19   $55.20   $55.20  
  Purchase #2 $249.47   7.563%   $268.3374   $268.34   $268.35   $268.30  
  Purchase #3 $162.28   3.598%   $168.1188   $168.12   $168.10   $168.10  
  Purchase #4 $9.96   13.510%   $11.3056   $11.31   $11.30   $11.30  
  Purchase #5 $143.79   12.421%   $161.6502   $161.65   $161.65   $161.70  
  Purchase #6 $52.37   7.403%   $56.247   $56.25   $56.25   $56.20  
  Purchase #7 $58.97   4.253%   $61.478   $61.48   $61.50   $61.50  
  7 purchase totals = $726.24       $782.3316   $782.34   $782.35   $782.30