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 $220.39   10.787%   $244.1635   $244.16   $244.15   $244.20  
  Purchase #2 $54.85   13.577%   $62.297   $62.30   $62.30   $62.30  
  Purchase #3 $35.28   10.424%   $38.9576   $38.96   $38.95   $39.00  
  Purchase #4 $181.41   13.758%   $206.3684   $206.37   $206.35   $206.40  
  Purchase #5 $53.54   5.707%   $56.5955   $56.60   $56.60   $56.60  
  Purchase #6 $174.71   13.694%   $198.6348   $198.63   $198.65   $198.60  
  Purchase #7 $137.95   11.654%   $154.0267   $154.03   $154.05   $154.00  
  7 purchase totals = $858.13       $961.0435   $961.05   $961.05   $961.10