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 $246.60   9.298%   $269.5289   $269.53   $269.55   $269.50  
  Purchase #2 $77.66   6.363%   $82.6015   $82.60   $82.60   $82.60  
  Purchase #3 $20.98   5.475%   $22.1287   $22.13   $22.15   $22.10  
  Purchase #4 $117.67   6.429%   $125.235   $125.24   $125.25   $125.20  
  Purchase #5 $118.70   4.256%   $123.7519   $123.75   $123.75   $123.80  
  Purchase #6 $225.65   4.147%   $235.0077   $235.01   $235.00   $235.00  
  Purchase #7 $91.38   9.273%   $99.8537   $99.85   $99.85   $99.90  
  7 purchase totals = $898.64       $958.1074   $958.11   $958.15   $958.10