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 $23.87   7.207%   $25.5903   $25.59   $25.60   $25.60  
  Purchase #2 $169.49   13.818%   $192.9101   $192.91   $192.90   $192.90  
  Purchase #3 $28.53   7.399%   $30.6409   $30.64   $30.65   $30.60  
  Purchase #4 $172.97   3.765%   $179.4823   $179.48   $179.50   $179.50  
  Purchase #5 $199.80   12.301%   $224.3774   $224.38   $224.40   $224.40  
  Purchase #6 $115.30   4.177%   $120.1161   $120.12   $120.10   $120.10  
  Purchase #7 $242.47   7.352%   $260.2964   $260.30   $260.30   $260.30  
  7 purchase totals = $952.43       $1,033.4135   $1,033.42   $1,033.45   $1,033.40