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 $195.67   8.158%   $211.6328   $211.63   $211.65   $211.60  
  Purchase #2 $89.94   7.334%   $96.5362   $96.54   $96.55   $96.50  
  Purchase #3 $140.84   3.650%   $145.9807   $145.98   $146.00   $146.00  
  Purchase #4 $101.41   11.803%   $113.3794   $113.38   $113.40   $113.40  
  Purchase #5 $165.83   5.631%   $175.1679   $175.17   $175.15   $175.20  
  Purchase #6 $186.74   10.792%   $206.893   $206.89   $206.90   $206.90  
  Purchase #7 $110.96   13.429%   $125.8608   $125.86   $125.85   $125.90  
  7 purchase totals = $991.39       $1,075.4508   $1,075.45   $1,075.50   $1,075.50