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 $153.46   7.692%   $165.2641   $165.26   $165.25   $165.30  
  Purchase #2 $172.68   8.575%   $187.4873   $187.49   $187.50   $187.50  
  Purchase #3 $146.40   7.757%   $157.7562   $157.76   $157.75   $157.80  
  Purchase #4 $59.96   4.391%   $62.5928   $62.59   $62.60   $62.60  
  Purchase #5 $187.47   7.838%   $202.1639   $202.16   $202.15   $202.20  
  Purchase #6 $17.77   8.583%   $19.2952   $19.30   $19.30   $19.30  
  Purchase #7 $238.83   13.783%   $271.7479   $271.75   $271.75   $271.70  
  7 purchase totals = $976.57       $1,066.3074   $1,066.31   $1,066.30   $1,066.40