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 $228.99   8.749%   $249.0243   $249.02   $249.00   $249.00  
  Purchase #2 $228.75   6.206%   $242.9462   $242.95   $242.95   $242.90  
  Purchase #3 $167.43   11.429%   $186.5656   $186.57   $186.55   $186.60  
  Purchase #4 $107.30   10.244%   $118.2918   $118.29   $118.30   $118.30  
  Purchase #5 $83.76   8.633%   $90.991   $90.99   $91.00   $91.00  
  Purchase #6 $10.58   3.750%   $10.9768   $10.98   $11.00   $11.00  
  Purchase #7 $116.39   6.796%   $124.2999   $124.30   $124.30   $124.30  
  7 purchase totals = $943.20       $1,023.0956   $1,023.10   $1,023.10   $1,023.10