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 $53.34   9.542%   $58.4297   $58.43   $58.45   $58.40  
  Purchase #2 $72.94   6.465%   $77.6556   $77.66   $77.65   $77.70  
  Purchase #3 $204.97   5.682%   $216.6164   $216.62   $216.60   $216.60  
  Purchase #4 $53.66   10.222%   $59.1451   $59.15   $59.15   $59.10  
  Purchase #5 $221.92   8.350%   $240.4503   $240.45   $240.45   $240.50  
  Purchase #6 $168.99   13.352%   $191.5535   $191.55   $191.55   $191.60  
  Purchase #7 $118.41   9.531%   $129.6957   $129.70   $129.70   $129.70  
  7 purchase totals = $894.23       $973.5463   $973.56   $973.55   $973.60