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 $91.41   6.617%   $97.4586   $97.46   $97.45   $97.50  
  Purchase #2 $244.66   9.373%   $267.592   $267.59   $267.60   $267.60  
  Purchase #3 $224.97   9.383%   $246.0789   $246.08   $246.10   $246.10  
  Purchase #4 $46.94   9.450%   $51.3758   $51.38   $51.40   $51.40  
  Purchase #5 $98.25   6.628%   $104.762   $104.76   $104.75   $104.80  
  Purchase #6 $248.73   6.313%   $264.4323   $264.43   $264.45   $264.40  
  Purchase #7 $156.89   12.274%   $176.1467   $176.15   $176.15   $176.10  
  7 purchase totals = $1,111.85       $1,207.8463   $1,207.85   $1,207.90   $1,207.90