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 $175.82   10.466%   $194.2213   $194.22   $194.20   $194.20  
  Purchase #2 $6.87   8.448%   $7.4504   $7.45   $7.45   $7.50  
  Purchase #3 $106.55   6.683%   $113.6707   $113.67   $113.65   $113.70  
  Purchase #4 $178.29   8.529%   $193.4964   $193.50   $193.50   $193.50  
  Purchase #5 $195.70   10.589%   $216.4227   $216.42   $216.40   $216.40  
  Purchase #6 $195.89   8.379%   $212.3036   $212.30   $212.30   $212.30  
  Purchase #7 $34.41   5.508%   $36.3053   $36.31   $36.30   $36.30  
  7 purchase totals = $893.53       $973.8704   $973.87   $973.80   $973.90