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 $141.97   3.313%   $146.6735   $146.67   $146.65   $146.70  
  Purchase #2 $188.28   8.103%   $203.5363   $203.54   $203.55   $203.50  
  Purchase #3 $156.36   13.265%   $177.1012   $177.10   $177.10   $177.10  
  Purchase #4 $193.50   8.653%   $210.2436   $210.24   $210.25   $210.20  
  Purchase #5 $241.87   4.623%   $253.0517   $253.05   $253.05   $253.10  
  Purchase #6 $247.60   13.687%   $281.489   $281.49   $281.50   $281.50  
  Purchase #7 $99.95   3.564%   $103.5122   $103.51   $103.50   $103.50  
  7 purchase totals = $1,269.53       $1,375.6075   $1,375.60   $1,375.60   $1,375.60