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 $237.66   9.403%   $260.0072   $260.01   $260.00   $260.00  
  Purchase #2 $246.25   12.791%   $277.7478   $277.75   $277.75   $277.70  
  Purchase #3 $245.33   12.242%   $275.3633   $275.36   $275.35   $275.40  
  Purchase #4 $41.38   8.504%   $44.899   $44.90   $44.90   $44.90  
  Purchase #5 $67.47   12.421%   $75.8504   $75.85   $75.85   $75.90  
  Purchase #6 $238.35   12.779%   $268.8087   $268.81   $268.80   $268.80  
  Purchase #7 $43.93   11.831%   $49.1274   $49.13   $49.15   $49.10  
  7 purchase totals = $1,120.37       $1,251.8038   $1,251.81   $1,251.80   $1,251.80