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 $49.47   3.814%   $51.3568   $51.36   $51.35   $51.40  
  Purchase #2 $214.33   12.367%   $240.8362   $240.84   $240.85   $240.80  
  Purchase #3 $51.96   7.119%   $55.659   $55.66   $55.65   $55.70  
  Purchase #4 $202.52   7.388%   $217.4822   $217.48   $217.50   $217.50  
  Purchase #5 $119.77   9.650%   $131.3278   $131.33   $131.35   $131.30  
  Purchase #6 $101.49   13.217%   $114.9039   $114.90   $114.90   $114.90  
  Purchase #7 $164.87   7.323%   $176.9434   $176.94   $176.95   $176.90  
  7 purchase totals = $904.41       $988.5093   $988.51   $988.55   $988.50