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 $27.53   11.634%   $30.7328   $30.73   $30.75   $30.70  
  Purchase #2 $52.44   4.662%   $54.8848   $54.88   $54.90   $54.90  
  Purchase #3 $177.64   11.850%   $198.6903   $198.69   $198.70   $198.70  
  Purchase #4 $81.49   13.667%   $92.6272   $92.63   $92.65   $92.60  
  Purchase #5 $118.70   9.700%   $130.2139   $130.21   $130.20   $130.20  
  Purchase #6 $109.30   12.123%   $122.5504   $122.55   $122.55   $122.60  
  Purchase #7 $123.98   6.686%   $132.2693   $132.27   $132.25   $132.30  
  7 purchase totals = $691.08       $761.9687   $761.96   $762.00   $762.00