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 $59.49   12.184%   $66.7383   $66.74   $66.75   $66.70  
  Purchase #2 $173.35   4.830%   $181.7228   $181.72   $181.70   $181.70  
  Purchase #3 $12.84   9.419%   $14.0494   $14.05   $14.05   $14.00  
  Purchase #4 $73.73   7.602%   $79.335   $79.34   $79.35   $79.30  
  Purchase #5 $93.88   12.457%   $105.5746   $105.57   $105.55   $105.60  
  Purchase #6 $219.97   9.491%   $240.8474   $240.85   $240.85   $240.80  
  Purchase #7 $207.54   9.472%   $227.1982   $227.20   $227.20   $227.20  
  7 purchase totals = $840.80       $915.4657   $915.47   $915.45   $915.30