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 $241.68   9.807%   $265.3816   $265.38   $265.40   $265.40  
  Purchase #2 $212.97   10.402%   $235.1231   $235.12   $235.10   $235.10  
  Purchase #3 $76.39   4.179%   $79.5823   $79.58   $79.60   $79.60  
  Purchase #4 $249.89   13.382%   $283.3303   $283.33   $283.35   $283.30  
  Purchase #5 $163.80   9.745%   $179.7623   $179.76   $179.75   $179.80  
  Purchase #6 $205.52   11.791%   $229.7529   $229.75   $229.75   $229.80  
  Purchase #7 $177.44   11.208%   $197.3275   $197.33   $197.35   $197.30  
  7 purchase totals = $1,327.69       $1,470.2600   $1,470.25   $1,470.30   $1,470.30