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 $83.89   12.493%   $94.3704   $94.37   $94.35   $94.40  
  Purchase #2 $77.51   4.582%   $81.0615   $81.06   $81.05   $81.10  
  Purchase #3 $132.33   3.131%   $136.4733   $136.47   $136.45   $136.50  
  Purchase #4 $122.50   8.203%   $132.5487   $132.55   $132.55   $132.50  
  Purchase #5 $213.29   12.565%   $240.0899   $240.09   $240.10   $240.10  
  Purchase #6 $190.48   11.572%   $212.5223   $212.52   $212.50   $212.50  
  Purchase #7 $120.35   3.799%   $124.9221   $124.92   $124.90   $124.90  
  7 purchase totals = $940.35       $1,021.9882   $1,021.98   $1,021.90   $1,022.00