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 $86.61   12.701%   $97.6103   $97.61   $97.60   $97.60  
  Purchase #2 $23.31   10.210%   $25.69   $25.69   $25.70   $25.70  
  Purchase #3 $237.51   9.186%   $259.3277   $259.33   $259.35   $259.30  
  Purchase #4 $173.67   5.116%   $182.555   $182.56   $182.55   $182.60  
  Purchase #5 $63.40   13.790%   $72.1429   $72.14   $72.15   $72.10  
  Purchase #6 $243.45   10.214%   $268.316   $268.32   $268.30   $268.30  
  Purchase #7 $161.27   11.165%   $179.2758   $179.28   $179.30   $179.30  
  7 purchase totals = $989.22       $1,084.9177   $1,084.93   $1,084.95   $1,084.90