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 $56.58   11.567%   $63.1246   $63.12   $63.10   $63.10  
  Purchase #2 $226.95   11.724%   $253.5576   $253.56   $253.55   $253.60  
  Purchase #3 $81.29   12.493%   $91.4456   $91.45   $91.45   $91.40  
  Purchase #4 $126.36   5.736%   $133.608   $133.61   $133.60   $133.60  
  Purchase #5 $78.84   7.655%   $84.8752   $84.88   $84.90   $84.90  
  Purchase #6 $22.77   9.231%   $24.8719   $24.87   $24.85   $24.90  
  Purchase #7 $191.46   10.122%   $210.8396   $210.84   $210.85   $210.80  
  7 purchase totals = $784.25       $862.3225   $862.33   $862.30   $862.30