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 $237.86   11.561%   $265.359   $265.36   $265.35   $265.40  
  Purchase #2 $189.75   11.654%   $211.8635   $211.86   $211.85   $211.90  
  Purchase #3 $216.57   11.289%   $241.0186   $241.02   $241.00   $241.00  
  Purchase #4 $36.82   13.622%   $41.8356   $41.84   $41.85   $41.80  
  Purchase #5 $102.62   10.429%   $113.3222   $113.32   $113.30   $113.30  
  Purchase #6 $118.82   12.587%   $133.7759   $133.78   $133.80   $133.80  
  Purchase #7 $30.29   13.198%   $34.2877   $34.29   $34.30   $34.30  
  7 purchase totals = $932.73       $1,041.4625   $1,041.47   $1,041.45   $1,041.50