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 $118.67   5.444%   $125.1304   $125.13   $125.15   $125.10  
  Purchase #2 $65.71   4.243%   $68.4981   $68.50   $68.50   $68.50  
  Purchase #3 $215.50   5.773%   $227.9408   $227.94   $227.95   $227.90  
  Purchase #4 $167.73   11.834%   $187.5792   $187.58   $187.60   $187.60  
  Purchase #5 $19.87   10.596%   $21.9754   $21.98   $22.00   $22.00  
  Purchase #6 $38.75   6.284%   $41.1851   $41.19   $41.20   $41.20  
  Purchase #7 $114.58   5.665%   $121.071   $121.07   $121.05   $121.10  
  7 purchase totals = $740.81       $793.3800   $793.39   $793.45   $793.40