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 $21.34   10.837%   $23.6526   $23.65   $23.65   $23.70  
  Purchase #2 $244.85   6.442%   $260.6232   $260.62   $260.60   $260.60  
  Purchase #3 $136.59   9.732%   $149.8829   $149.88   $149.90   $149.90  
  Purchase #4 $226.88   11.596%   $253.189   $253.19   $253.20   $253.20  
  Purchase #5 $143.57   11.772%   $160.4711   $160.47   $160.45   $160.50  
  Purchase #6 $20.91   6.313%   $22.23   $22.23   $22.25   $22.20  
  Purchase #7 $239.91   13.590%   $272.5138   $272.51   $272.50   $272.50  
  7 purchase totals = $1,034.05       $1,142.5626   $1,142.55   $1,142.55   $1,142.60