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 $186.52   4.118%   $194.2009   $194.20   $194.20   $194.20  
  Purchase #2 $18.83   8.191%   $20.3724   $20.37   $20.35   $20.40  
  Purchase #3 $153.93   4.663%   $161.1078   $161.11   $161.10   $161.10  
  Purchase #4 $15.71   7.119%   $16.8284   $16.83   $16.85   $16.80  
  Purchase #5 $228.29   8.513%   $247.7243   $247.72   $247.70   $247.70  
  Purchase #6 $107.83   6.273%   $114.5942   $114.59   $114.60   $114.60  
  Purchase #7 $72.34   6.520%   $77.0566   $77.06   $77.05   $77.10  
  7 purchase totals = $783.45       $831.8846   $831.88   $831.85   $831.90