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 $216.56   11.788%   $242.0881   $242.09   $242.10   $242.10  
  Purchase #2 $102.74   9.661%   $112.6657   $112.67   $112.65   $112.70  
  Purchase #3 $205.90   3.331%   $212.7585   $212.76   $212.75   $212.80  
  Purchase #4 $175.92   9.593%   $192.796   $192.80   $192.80   $192.80  
  Purchase #5 $102.34   10.743%   $113.3344   $113.33   $113.35   $113.30  
  Purchase #6 $138.26   3.299%   $142.8212   $142.82   $142.80   $142.80  
  Purchase #7 $230.34   3.112%   $237.5082   $237.51   $237.50   $237.50  
  7 purchase totals = $1,172.06       $1,253.9721   $1,253.98   $1,253.95   $1,254.00