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 $62.30   10.145%   $68.6203   $68.62   $68.60   $68.60  
  Purchase #2 $127.77   13.820%   $145.4278   $145.43   $145.45   $145.40  
  Purchase #3 $185.34   11.267%   $206.2223   $206.22   $206.20   $206.20  
  Purchase #4 $85.86   7.237%   $92.0737   $92.07   $92.05   $92.10  
  Purchase #5 $247.87   10.414%   $273.6832   $273.68   $273.70   $273.70  
  Purchase #6 $164.67   12.862%   $185.8499   $185.85   $185.85   $185.80  
  Purchase #7 $138.58   11.705%   $154.8008   $154.80   $154.80   $154.80  
  7 purchase totals = $1,012.39       $1,126.6780   $1,126.67   $1,126.65   $1,126.60