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 $40.52   7.473%   $43.5481   $43.55   $43.55   $43.50  
  Purchase #2 $46.55   3.215%   $48.0466   $48.05   $48.05   $48.00  
  Purchase #3 $244.61   11.744%   $273.337   $273.34   $273.35   $273.30  
  Purchase #4 $248.38   10.795%   $275.1926   $275.19   $275.20   $275.20  
  Purchase #5 $219.78   12.359%   $246.9426   $246.94   $246.95   $246.90  
  Purchase #6 $22.76   11.639%   $25.409   $25.41   $25.40   $25.40  
  Purchase #7 $238.84   4.556%   $249.7216   $249.72   $249.70   $249.70  
  7 purchase totals = $1,061.44       $1,162.1975   $1,162.20   $1,162.20   $1,162.00