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 $191.67   5.337%   $201.8994   $201.90   $201.90   $201.90  
  Purchase #2 $79.82   7.314%   $85.658   $85.66   $85.65   $85.70  
  Purchase #3 $71.85   6.263%   $76.35   $76.35   $76.35   $76.40  
  Purchase #4 $109.86   10.402%   $121.2876   $121.29   $121.30   $121.30  
  Purchase #5 $114.84   6.547%   $122.3586   $122.36   $122.35   $122.40  
  Purchase #6 $43.28   7.145%   $46.3724   $46.37   $46.35   $46.40  
  Purchase #7 $164.88   12.140%   $184.8964   $184.90   $184.90   $184.90  
  7 purchase totals = $776.20       $838.8224   $838.83   $838.80   $839.00