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 $60.31   13.381%   $68.3801   $68.38   $68.40   $68.40  
  Purchase #2 $98.49   4.305%   $102.73   $102.73   $102.75   $102.70  
  Purchase #3 $180.45   13.418%   $204.6628   $204.66   $204.65   $204.70  
  Purchase #4 $60.32   7.372%   $64.7668   $64.77   $64.75   $64.80  
  Purchase #5 $198.58   10.704%   $219.836   $219.84   $219.85   $219.80  
  Purchase #6 $109.60   8.618%   $119.0453   $119.05   $119.05   $119.00  
  Purchase #7 $122.89   10.159%   $135.3744   $135.37   $135.35   $135.40  
  7 purchase totals = $830.64       $914.7954   $914.80   $914.80   $914.80