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 $54.98   8.656%   $59.7391   $59.74   $59.75   $59.70  
  Purchase #2 $97.54   8.673%   $105.9996   $106.00   $106.00   $106.00  
  Purchase #3 $25.69   7.571%   $27.635   $27.64   $27.65   $27.60  
  Purchase #4 $216.46   12.363%   $243.2209   $243.22   $243.20   $243.20  
  Purchase #5 $26.92   12.498%   $30.2845   $30.28   $30.30   $30.30  
  Purchase #6 $250.40   13.247%   $283.5705   $283.57   $283.55   $283.60  
  Purchase #7 $137.37   13.798%   $156.3243   $156.32   $156.30   $156.30  
  7 purchase totals = $809.36       $906.7739   $906.77   $906.75   $906.70