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 $76.51   13.148%   $86.5695   $86.57   $86.55   $86.60  
  Purchase #2 $47.78   3.776%   $49.5842   $49.58   $49.60   $49.60  
  Purchase #3 $135.37   9.679%   $148.4725   $148.47   $148.45   $148.50  
  Purchase #4 $150.47   4.363%   $157.035   $157.04   $157.05   $157.00  
  Purchase #5 $127.80   10.446%   $141.15   $141.15   $141.15   $141.20  
  Purchase #6 $205.61   7.199%   $220.4119   $220.41   $220.40   $220.40  
  Purchase #7 $241.84   13.559%   $274.6311   $274.63   $274.65   $274.60  
  7 purchase totals = $985.38       $1,077.8542   $1,077.85   $1,077.85   $1,077.90