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 $61.51   6.711%   $65.6379   $65.64   $65.65   $65.60  
  Purchase #2 $154.85   5.211%   $162.9192   $162.92   $162.90   $162.90  
  Purchase #3 $209.42   6.627%   $223.2983   $223.30   $223.30   $223.30  
  Purchase #4 $167.37   13.806%   $190.4771   $190.48   $190.50   $190.50  
  Purchase #5 $125.26   9.820%   $137.5605   $137.56   $137.55   $137.60  
  Purchase #6 $136.49   12.355%   $153.3533   $153.35   $153.35   $153.40  
  Purchase #7 $189.57   6.659%   $202.1935   $202.19   $202.20   $202.20  
  7 purchase totals = $1,044.47       $1,135.4398   $1,135.44   $1,135.45   $1,135.50