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 $237.34   12.497%   $267.0004   $267.00   $267.00   $267.00  
  Purchase #2 $228.49   3.274%   $235.9708   $235.97   $235.95   $236.00  
  Purchase #3 $247.52   8.428%   $268.381   $268.38   $268.40   $268.40  
  Purchase #4 $53.47   9.376%   $58.4833   $58.48   $58.50   $58.50  
  Purchase #5 $73.97   11.752%   $82.663   $82.66   $82.65   $82.70  
  Purchase #6 $87.97   13.127%   $99.5178   $99.52   $99.50   $99.50  
  Purchase #7 $145.85   12.710%   $164.3875   $164.39   $164.40   $164.40  
  7 purchase totals = $1,074.61       $1,176.4038   $1,176.40   $1,176.40   $1,176.50