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 $59.55   11.810%   $66.5829   $66.58   $66.60   $66.60  
  Purchase #2 $227.74   3.838%   $236.4807   $236.48   $236.50   $236.50  
  Purchase #3 $44.35   7.651%   $47.7432   $47.74   $47.75   $47.70  
  Purchase #4 $23.27   8.472%   $25.2414   $25.24   $25.25   $25.20  
  Purchase #5 $250.33   10.188%   $275.8336   $275.83   $275.85   $275.80  
  Purchase #6 $232.65   6.415%   $247.5745   $247.57   $247.55   $247.60  
  Purchase #7 $239.47   13.303%   $271.3267   $271.33   $271.35   $271.30  
  7 purchase totals = $1,077.36       $1,170.7830   $1,170.77   $1,170.85   $1,170.70