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 $193.54   5.792%   $204.7498   $204.75   $204.75   $204.70  
  Purchase #2 $21.26   5.643%   $22.4597   $22.46   $22.45   $22.50  
  Purchase #3 $246.61   3.418%   $255.0391   $255.04   $255.05   $255.00  
  Purchase #4 $103.44   11.803%   $115.649   $115.65   $115.65   $115.60  
  Purchase #5 $217.39   3.865%   $225.7921   $225.79   $225.80   $225.80  
  Purchase #6 $60.44   13.742%   $68.7457   $68.75   $68.75   $68.70  
  Purchase #7 $58.64   13.644%   $66.6408   $66.64   $66.65   $66.60  
  7 purchase totals = $901.32       $959.0762   $959.08   $959.10   $958.90