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 $41.74   12.343%   $46.892   $46.89   $46.90   $46.90  
  Purchase #2 $171.43   5.344%   $180.5912   $180.59   $180.60   $180.60  
  Purchase #3 $50.80   11.324%   $56.5526   $56.55   $56.55   $56.60  
  Purchase #4 $161.82   6.769%   $172.7736   $172.77   $172.75   $172.80  
  Purchase #5 $205.63   5.193%   $216.3084   $216.31   $216.30   $216.30  
  Purchase #6 $145.76   5.444%   $153.6952   $153.70   $153.70   $153.70  
  Purchase #7 $11.85   10.464%   $13.09   $13.09   $13.10   $13.10  
  7 purchase totals = $789.03       $839.9030   $839.90   $839.90   $840.00