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 $218.95   3.650%   $226.9417   $226.94   $226.95   $226.90  
  Purchase #2 $54.33   3.670%   $56.3239   $56.32   $56.30   $56.30  
  Purchase #3 $96.98   10.531%   $107.193   $107.19   $107.20   $107.20  
  Purchase #4 $126.26   7.191%   $135.3394   $135.34   $135.35   $135.30  
  Purchase #5 $98.47   7.183%   $105.5431   $105.54   $105.55   $105.50  
  Purchase #6 $217.79   11.518%   $242.8751   $242.88   $242.90   $242.90  
  Purchase #7 $159.69   10.367%   $176.2451   $176.25   $176.25   $176.20  
  7 purchase totals = $972.47       $1,050.4613   $1,050.46   $1,050.50   $1,050.30