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 $56.74   3.545%   $58.7514   $58.75   $58.75   $58.80  
  Purchase #2 $68.76   6.450%   $73.195   $73.20   $73.20   $73.20  
  Purchase #3 $150.79   3.277%   $155.7314   $155.73   $155.75   $155.70  
  Purchase #4 $203.72   6.409%   $216.7764   $216.78   $216.80   $216.80  
  Purchase #5 $95.95   5.641%   $101.3625   $101.36   $101.35   $101.40  
  Purchase #6 $216.79   8.289%   $234.7597   $234.76   $234.75   $234.80  
  Purchase #7 $153.90   3.739%   $159.6543   $159.65   $159.65   $159.70  
  7 purchase totals = $946.65       $1,000.2307   $1,000.23   $1,000.25   $1,000.40