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 $87.77   6.633%   $93.5918   $93.59   $93.60   $93.60  
  Purchase #2 $146.99   10.310%   $162.1447   $162.14   $162.15   $162.10  
  Purchase #3 $9.35   13.349%   $10.5981   $10.60   $10.60   $10.60  
  Purchase #4 $195.62   10.444%   $216.0506   $216.05   $216.05   $216.10  
  Purchase #5 $104.32   3.710%   $108.1903   $108.19   $108.20   $108.20  
  Purchase #6 $198.72   9.628%   $217.8528   $217.85   $217.85   $217.90  
  Purchase #7 $110.68   6.341%   $117.6982   $117.70   $117.70   $117.70  
  7 purchase totals = $853.45       $926.1265   $926.12   $926.15   $926.20