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 $58.32   12.751%   $65.7564   $65.76   $65.75   $65.80  
  Purchase #2 $184.52   9.757%   $202.5236   $202.52   $202.50   $202.50  
  Purchase #3 $163.56   11.710%   $182.7129   $182.71   $182.70   $182.70  
  Purchase #4 $191.65   9.747%   $210.3301   $210.33   $210.35   $210.30  
  Purchase #5 $231.45   5.475%   $244.1219   $244.12   $244.10   $244.10  
  Purchase #6 $247.37   13.617%   $281.0544   $281.05   $281.05   $281.10  
  Purchase #7 $133.46   9.219%   $145.7637   $145.76   $145.75   $145.80  
  7 purchase totals = $1,210.33       $1,332.2630   $1,332.25   $1,332.20   $1,332.30