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 $77.39   8.212%   $83.7453   $83.75   $83.75   $83.70  
  Purchase #2 $57.47   4.576%   $60.0998   $60.10   $60.10   $60.10  
  Purchase #3 $234.96   12.612%   $264.5932   $264.59   $264.60   $264.60  
  Purchase #4 $24.57   4.573%   $25.6936   $25.69   $25.70   $25.70  
  Purchase #5 $115.56   12.249%   $129.7149   $129.71   $129.70   $129.70  
  Purchase #6 $245.89   13.794%   $279.8081   $279.81   $279.80   $279.80  
  Purchase #7 $208.82   8.672%   $226.9289   $226.93   $226.95   $226.90  
  7 purchase totals = $964.66       $1,070.5838   $1,070.58   $1,070.60   $1,070.50