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 $93.87   9.258%   $102.5605   $102.56   $102.55   $102.60  
  Purchase #2 $181.60   7.195%   $194.6661   $194.67   $194.65   $194.70  
  Purchase #3 $15.99   13.480%   $18.1455   $18.15   $18.15   $18.10  
  Purchase #4 $173.43   5.202%   $182.4518   $182.45   $182.45   $182.50  
  Purchase #5 $60.41   6.564%   $64.3753   $64.38   $64.40   $64.40  
  Purchase #6 $201.88   4.261%   $210.4821   $210.48   $210.50   $210.50  
  Purchase #7 $165.89   9.430%   $181.5334   $181.53   $181.55   $181.50  
  7 purchase totals = $893.07       $954.2147   $954.22   $954.25   $954.30