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 $61.48   9.130%   $67.0931   $67.09   $67.10   $67.10  
  Purchase #2 $194.63   11.817%   $217.6294   $217.63   $217.65   $217.60  
  Purchase #3 $245.44   12.570%   $276.2918   $276.29   $276.30   $276.30  
  Purchase #4 $58.98   9.763%   $64.7382   $64.74   $64.75   $64.70  
  Purchase #5 $88.78   6.171%   $94.2586   $94.26   $94.25   $94.30  
  Purchase #6 $131.66   11.123%   $146.3045   $146.30   $146.30   $146.30  
  Purchase #7 $55.47   10.702%   $61.4064   $61.41   $61.40   $61.40  
  7 purchase totals = $836.44       $927.7220   $927.72   $927.75   $927.70