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 $183.27   10.739%   $202.9514   $202.95   $202.95   $203.00  
  Purchase #2 $112.78   11.214%   $125.4271   $125.43   $125.45   $125.40  
  Purchase #3 $148.26   10.328%   $163.5723   $163.57   $163.55   $163.60  
  Purchase #4 $235.39   5.863%   $249.1909   $249.19   $249.20   $249.20  
  Purchase #5 $79.44   11.468%   $88.5502   $88.55   $88.55   $88.60  
  Purchase #6 $138.74   9.637%   $152.1104   $152.11   $152.10   $152.10  
  Purchase #7 $108.83   5.538%   $114.857   $114.86   $114.85   $114.90  
  7 purchase totals = $1,006.71       $1,096.6593   $1,096.66   $1,096.65   $1,096.80