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 $54.90   8.480%   $59.5555   $59.56   $59.55   $59.60  
  Purchase #2 $188.80   8.364%   $204.5912   $204.59   $204.60   $204.60  
  Purchase #3 $187.55   10.252%   $206.7776   $206.78   $206.80   $206.80  
  Purchase #4 $148.44   4.533%   $155.1688   $155.17   $155.15   $155.20  
  Purchase #5 $85.81   8.691%   $93.2677   $93.27   $93.25   $93.30  
  Purchase #6 $204.40   11.626%   $228.1635   $228.16   $228.15   $228.20  
  Purchase #7 $23.28   11.597%   $25.9798   $25.98   $26.00   $26.00  
  7 purchase totals = $893.18       $973.5041   $973.51   $973.50   $973.70