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 $176.84   8.161%   $191.2719   $191.27   $191.25   $191.30  
  Purchase #2 $232.61   13.581%   $264.2008   $264.20   $264.20   $264.20  
  Purchase #3 $12.29   10.382%   $13.5659   $13.57   $13.55   $13.60  
  Purchase #4 $206.73   4.200%   $215.4127   $215.41   $215.40   $215.40  
  Purchase #5 $207.54   12.869%   $234.2483   $234.25   $234.25   $234.20  
  Purchase #6 $84.33   5.365%   $88.8543   $88.85   $88.85   $88.90  
  Purchase #7 $65.40   6.514%   $69.6602   $69.66   $69.65   $69.70  
  7 purchase totals = $985.74       $1,077.2141   $1,077.21   $1,077.15   $1,077.30