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 $85.57   12.401%   $96.1815   $96.18   $96.20   $96.20  
  Purchase #2 $103.86   9.575%   $113.8046   $113.80   $113.80   $113.80  
  Purchase #3 $238.92   5.208%   $251.363   $251.36   $251.35   $251.40  
  Purchase #4 $129.87   7.357%   $139.4245   $139.42   $139.40   $139.40  
  Purchase #5 $104.45   10.254%   $115.1603   $115.16   $115.15   $115.20  
  Purchase #6 $208.87   7.126%   $223.7541   $223.75   $223.75   $223.80  
  Purchase #7 $5.87   11.225%   $6.5289   $6.53   $6.55   $6.50  
  7 purchase totals = $877.41       $946.2169   $946.20   $946.20   $946.30