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 $46.29   8.685%   $50.3103   $50.31   $50.30   $50.30  
  Purchase #2 $149.78   9.520%   $164.0391   $164.04   $164.05   $164.00  
  Purchase #3 $59.66   8.563%   $64.7687   $64.77   $64.75   $64.80  
  Purchase #4 $114.41   9.212%   $124.9494   $124.95   $124.95   $124.90  
  Purchase #5 $236.97   3.752%   $245.8611   $245.86   $245.85   $245.90  
  Purchase #6 $199.87   6.211%   $212.2839   $212.28   $212.30   $212.30  
  Purchase #7 $134.40   8.240%   $145.4746   $145.47   $145.45   $145.50  
  7 purchase totals = $941.38       $1,007.6871   $1,007.68   $1,007.65   $1,007.70