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 $158.65   10.731%   $175.6747   $175.67   $175.65   $175.70  
  Purchase #2 $161.64   5.735%   $170.9101   $170.91   $170.90   $170.90  
  Purchase #3 $34.63   6.506%   $36.883   $36.88   $36.90   $36.90  
  Purchase #4 $147.35   3.635%   $152.7062   $152.71   $152.70   $152.70  
  Purchase #5 $52.40   13.709%   $59.5835   $59.58   $59.60   $59.60  
  Purchase #6 $22.53   12.846%   $25.4242   $25.42   $25.40   $25.40  
  Purchase #7 $85.89   7.694%   $92.4984   $92.50   $92.50   $92.50  
  7 purchase totals = $663.09       $713.6801   $713.67   $713.65   $713.70