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 $246.85   8.782%   $268.5284   $268.53   $268.55   $268.50  
  Purchase #2 $93.97   4.508%   $98.2062   $98.21   $98.20   $98.20  
  Purchase #3 $240.77   12.797%   $271.5813   $271.58   $271.60   $271.60  
  Purchase #4 $121.73   12.365%   $136.7819   $136.78   $136.80   $136.80  
  Purchase #5 $177.51   12.861%   $200.3396   $200.34   $200.35   $200.30  
  Purchase #6 $50.65   8.517%   $54.9639   $54.96   $54.95   $55.00  
  Purchase #7 $39.30   10.365%   $43.3734   $43.37   $43.35   $43.40  
  7 purchase totals = $970.78       $1,073.7747   $1,073.77   $1,073.80   $1,073.80