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 $170.26   11.111%   $189.1776   $189.18   $189.20   $189.20  
  Purchase #2 $196.38   6.182%   $208.5202   $208.52   $208.50   $208.50  
  Purchase #3 $147.70   12.109%   $165.585   $165.59   $165.60   $165.60  
  Purchase #4 $114.72   6.460%   $122.1309   $122.13   $122.15   $122.10  
  Purchase #5 $213.31   13.843%   $242.8385   $242.84   $242.85   $242.80  
  Purchase #6 $147.36   5.857%   $155.9909   $155.99   $156.00   $156.00  
  Purchase #7 $78.44   4.555%   $82.0129   $82.01   $82.00   $82.00  
  7 purchase totals = $1,068.17       $1,166.2560   $1,166.26   $1,166.30   $1,166.20