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 $25.71   10.860%   $28.5021   $28.50   $28.50   $28.50  
  Purchase #2 $92.71   3.109%   $95.5924   $95.59   $95.60   $95.60  
  Purchase #3 $154.65   13.502%   $175.5308   $175.53   $175.55   $175.50  
  Purchase #4 $233.79   5.804%   $247.3592   $247.36   $247.35   $247.40  
  Purchase #5 $188.96   8.228%   $204.5076   $204.51   $204.50   $204.50  
  Purchase #6 $220.31   6.863%   $235.4299   $235.43   $235.45   $235.40  
  Purchase #7 $71.90   3.237%   $74.2274   $74.23   $74.25   $74.20  
  7 purchase totals = $988.03       $1,061.1494   $1,061.15   $1,061.20   $1,061.10