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 $91.30   4.868%   $95.7445   $95.74   $95.75   $95.70  
  Purchase #2 $90.44   12.358%   $101.6166   $101.62   $101.60   $101.60  
  Purchase #3 $184.69   11.729%   $206.3523   $206.35   $206.35   $206.40  
  Purchase #4 $30.98   4.216%   $32.2861   $32.29   $32.30   $32.30  
  Purchase #5 $28.97   13.514%   $32.885   $32.89   $32.90   $32.90  
  Purchase #6 $219.53   3.157%   $226.4606   $226.46   $226.45   $226.50  
  Purchase #7 $103.83   6.216%   $110.2841   $110.28   $110.30   $110.30  
  7 purchase totals = $749.74       $805.6292   $805.63   $805.65   $805.70