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 $54.45   7.718%   $58.6525   $58.65   $58.65   $58.70  
  Purchase #2 $143.52   12.146%   $160.9519   $160.95   $160.95   $161.00  
  Purchase #3 $250.29   13.596%   $284.3194   $284.32   $284.30   $284.30  
  Purchase #4 $197.45   13.140%   $223.3949   $223.39   $223.40   $223.40  
  Purchase #5 $231.65   9.380%   $253.3788   $253.38   $253.40   $253.40  
  Purchase #6 $158.75   3.687%   $164.6031   $164.60   $164.60   $164.60  
  Purchase #7 $103.41   11.728%   $115.5379   $115.54   $115.55   $115.50  
  7 purchase totals = $1,139.52       $1,260.8385   $1,260.83   $1,260.85   $1,260.90