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 $194.37   4.293%   $202.7143   $202.71   $202.70   $202.70  
  Purchase #2 $5.62   12.620%   $6.3292   $6.33   $6.35   $6.30  
  Purchase #3 $114.70   9.554%   $125.6584   $125.66   $125.65   $125.70  
  Purchase #4 $164.74   11.821%   $184.2139   $184.21   $184.20   $184.20  
  Purchase #5 $221.35   6.863%   $236.5413   $236.54   $236.55   $236.50  
  Purchase #6 $218.98   11.672%   $244.5393   $244.54   $244.55   $244.50  
  Purchase #7 $82.97   12.282%   $93.1604   $93.16   $93.15   $93.20  
  7 purchase totals = $1,002.73       $1,093.1568   $1,093.15   $1,093.15   $1,093.10