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 $244.73   9.561%   $268.1286   $268.13   $268.15   $268.10  
  Purchase #2 $31.85   7.389%   $34.2034   $34.20   $34.20   $34.20  
  Purchase #3 $229.59   12.437%   $258.1441   $258.14   $258.15   $258.10  
  Purchase #4 $208.68   5.374%   $219.8945   $219.89   $219.90   $219.90  
  Purchase #5 $246.44   9.354%   $269.492   $269.49   $269.50   $269.50  
  Purchase #6 $66.96   13.110%   $75.7385   $75.74   $75.75   $75.70  
  Purchase #7 $170.66   5.586%   $180.1931   $180.19   $180.20   $180.20  
  7 purchase totals = $1,198.91       $1,305.7942   $1,305.78   $1,305.85   $1,305.70