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 $121.94   8.212%   $131.9537   $131.95   $131.95   $132.00  
  Purchase #2 $216.69   9.800%   $237.9256   $237.93   $237.95   $237.90  
  Purchase #3 $17.45   5.575%   $18.4228   $18.42   $18.40   $18.40  
  Purchase #4 $140.85   9.524%   $154.2646   $154.26   $154.25   $154.30  
  Purchase #5 $237.29   13.636%   $269.6469   $269.65   $269.65   $269.60  
  Purchase #6 $209.44   12.625%   $235.8818   $235.88   $235.90   $235.90  
  Purchase #7 $117.85   13.212%   $133.4203   $133.42   $133.40   $133.40  
  7 purchase totals = $1,061.51       $1,181.5157   $1,181.51   $1,181.50   $1,181.50