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 $84.83   10.234%   $93.5115   $93.51   $93.50   $93.50  
  Purchase #2 $192.62   6.569%   $205.2732   $205.27   $205.25   $205.30  
  Purchase #3 $41.31   5.255%   $43.4808   $43.48   $43.50   $43.50  
  Purchase #4 $78.68   9.308%   $86.0035   $86.00   $86.00   $86.00  
  Purchase #5 $217.99   9.162%   $237.9622   $237.96   $237.95   $238.00  
  Purchase #6 $198.55   5.462%   $209.3948   $209.39   $209.40   $209.40  
  Purchase #7 $247.61   10.568%   $273.7774   $273.78   $273.80   $273.80  
  7 purchase totals = $1,061.59       $1,149.4034   $1,149.39   $1,149.40   $1,149.50