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 $236.25   4.694%   $247.3396   $247.34   $247.35   $247.30  
  Purchase #2 $178.78   3.832%   $185.6308   $185.63   $185.65   $185.60  
  Purchase #3 $80.61   5.183%   $84.788   $84.79   $84.80   $84.80  
  Purchase #4 $183.96   4.485%   $192.2106   $192.21   $192.20   $192.20  
  Purchase #5 $82.75   7.867%   $89.2599   $89.26   $89.25   $89.30  
  Purchase #6 $91.45   11.191%   $101.6842   $101.68   $101.70   $101.70  
  Purchase #7 $53.34   3.531%   $55.2234   $55.22   $55.20   $55.20  
  7 purchase totals = $907.14       $956.1365   $956.13   $956.15   $956.10