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 $175.84   13.567%   $199.6962   $199.70   $199.70   $199.70  
  Purchase #2 $166.29   8.354%   $180.1819   $180.18   $180.20   $180.20  
  Purchase #3 $235.75   3.616%   $244.2747   $244.27   $244.25   $244.30  
  Purchase #4 $99.53   11.384%   $110.8605   $110.86   $110.85   $110.90  
  Purchase #5 $247.43   12.604%   $278.6161   $278.62   $278.60   $278.60  
  Purchase #6 $188.55   5.354%   $198.645   $198.65   $198.65   $198.60  
  Purchase #7 $105.46   8.508%   $114.4325   $114.43   $114.45   $114.40  
  7 purchase totals = $1,218.85       $1,326.7069   $1,326.71   $1,326.70   $1,326.70