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 $41.34   8.123%   $44.698   $44.70   $44.70   $44.70  
  Purchase #2 $169.42   8.402%   $183.6547   $183.65   $183.65   $183.70  
  Purchase #3 $163.39   8.672%   $177.5592   $177.56   $177.55   $177.60  
  Purchase #4 $248.87   7.374%   $267.2217   $267.22   $267.20   $267.20  
  Purchase #5 $128.25   12.417%   $144.1748   $144.17   $144.15   $144.20  
  Purchase #6 $93.64   9.252%   $102.3036   $102.30   $102.30   $102.30  
  Purchase #7 $133.73   9.215%   $146.0532   $146.05   $146.05   $146.10  
  7 purchase totals = $978.64       $1,065.6652   $1,065.65   $1,065.60   $1,065.80