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 $227.51   9.144%   $248.3135   $248.31   $248.30   $248.30  
  Purchase #2 $241.63   3.304%   $249.6135   $249.61   $249.60   $249.60  
  Purchase #3 $104.75   12.297%   $117.6311   $117.63   $117.65   $117.60  
  Purchase #4 $199.70   12.410%   $224.4828   $224.48   $224.50   $224.50  
  Purchase #5 $59.43   6.451%   $63.2638   $63.26   $63.25   $63.30  
  Purchase #6 $183.78   11.301%   $204.549   $204.55   $204.55   $204.50  
  Purchase #7 $79.48   5.338%   $83.7226   $83.72   $83.70   $83.70  
  7 purchase totals = $1,096.28       $1,191.5763   $1,191.56   $1,191.55   $1,191.50