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 $243.29   9.612%   $266.675   $266.68   $266.70   $266.70  
  Purchase #2 $91.95   11.762%   $102.7652   $102.77   $102.75   $102.80  
  Purchase #3 $50.73   9.832%   $55.7178   $55.72   $55.70   $55.70  
  Purchase #4 $148.67   8.297%   $161.0051   $161.01   $161.00   $161.00  
  Purchase #5 $107.47   10.533%   $118.7898   $118.79   $118.80   $118.80  
  Purchase #6 $233.98   8.748%   $254.4486   $254.45   $254.45   $254.40  
  Purchase #7 $149.44   11.762%   $167.0171   $167.02   $167.00   $167.00  
  7 purchase totals = $1,025.53       $1,126.4186   $1,126.44   $1,126.40   $1,126.40