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 $199.49   8.843%   $217.1309   $217.13   $217.15   $217.10  
  Purchase #2 $109.77   7.226%   $117.702   $117.70   $117.70   $117.70  
  Purchase #3 $235.96   13.220%   $267.1539   $267.15   $267.15   $267.20  
  Purchase #4 $180.58   4.508%   $188.7205   $188.72   $188.70   $188.70  
  Purchase #5 $145.55   4.309%   $151.8217   $151.82   $151.80   $151.80  
  Purchase #6 $34.77   6.573%   $37.0554   $37.06   $37.05   $37.10  
  Purchase #7 $228.59   13.223%   $258.8165   $258.82   $258.80   $258.80  
  7 purchase totals = $1,134.71       $1,238.4009   $1,238.40   $1,238.35   $1,238.40