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 $208.48   7.327%   $223.7553   $223.76   $223.75   $223.80  
  Purchase #2 $196.74   6.452%   $209.4337   $209.43   $209.45   $209.40  
  Purchase #3 $50.64   11.611%   $56.5198   $56.52   $56.50   $56.50  
  Purchase #4 $177.99   9.384%   $194.6926   $194.69   $194.70   $194.70  
  Purchase #5 $32.50   3.184%   $33.5348   $33.53   $33.55   $33.50  
  Purchase #6 $21.59   7.659%   $23.2436   $23.24   $23.25   $23.20  
  Purchase #7 $60.54   11.273%   $67.3647   $67.36   $67.35   $67.40  
  7 purchase totals = $748.48       $808.5445   $808.53   $808.55   $808.50