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 $82.26   4.236%   $85.7445   $85.74   $85.75   $85.70  
  Purchase #2 $177.80   9.616%   $194.8972   $194.90   $194.90   $194.90  
  Purchase #3 $5.62   3.616%   $5.8232   $5.82   $5.80   $5.80  
  Purchase #4 $242.28   13.753%   $275.6008   $275.60   $275.60   $275.60  
  Purchase #5 $119.40   13.232%   $135.199   $135.20   $135.20   $135.20  
  Purchase #6 $43.48   6.429%   $46.2753   $46.28   $46.30   $46.30  
  Purchase #7 $207.30   3.635%   $214.8354   $214.84   $214.85   $214.80  
  7 purchase totals = $878.14       $958.3754   $958.38   $958.40   $958.30