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 $113.88   3.795%   $118.2017   $118.20   $118.20   $118.20  
  Purchase #2 $243.38   5.709%   $257.2746   $257.27   $257.25   $257.30  
  Purchase #3 $162.62   10.647%   $179.9342   $179.93   $179.95   $179.90  
  Purchase #4 $77.65   9.165%   $84.7666   $84.77   $84.75   $84.80  
  Purchase #5 $56.62   12.329%   $63.6007   $63.60   $63.60   $63.60  
  Purchase #6 $205.98   3.662%   $213.523   $213.52   $213.50   $213.50  
  Purchase #7 $159.69   13.545%   $181.32   $181.32   $181.30   $181.30  
  7 purchase totals = $1,019.82       $1,098.6208   $1,098.61   $1,098.55   $1,098.60