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 $244.71   12.168%   $274.4863   $274.49   $274.50   $274.50  
  Purchase #2 $192.97   3.288%   $199.3149   $199.31   $199.30   $199.30  
  Purchase #3 $45.90   11.864%   $51.3456   $51.35   $51.35   $51.30  
  Purchase #4 $157.79   9.474%   $172.739   $172.74   $172.75   $172.70  
  Purchase #5 $45.70   7.501%   $49.128   $49.13   $49.15   $49.10  
  Purchase #6 $68.59   13.627%   $77.9368   $77.94   $77.95   $77.90  
  Purchase #7 $209.58   12.653%   $236.0982   $236.10   $236.10   $236.10  
  7 purchase totals = $965.24       $1,061.0488   $1,061.06   $1,061.10   $1,060.90