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 $41.98   10.402%   $46.3468   $46.35   $46.35   $46.30  
  Purchase #2 $96.74   13.300%   $109.6064   $109.61   $109.60   $109.60  
  Purchase #3 $128.57   6.604%   $137.0608   $137.06   $137.05   $137.10  
  Purchase #4 $64.99   8.343%   $70.4121   $70.41   $70.40   $70.40  
  Purchase #5 $143.48   5.737%   $151.7114   $151.71   $151.70   $151.70  
  Purchase #6 $103.66   6.230%   $110.118   $110.12   $110.10   $110.10  
  Purchase #7 $214.66   9.156%   $234.3143   $234.31   $234.30   $234.30  
  7 purchase totals = $794.08       $859.5698   $859.57   $859.50   $859.50