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 $120.94   11.541%   $134.8977   $134.90   $134.90   $134.90  
  Purchase #2 $54.57   8.578%   $59.251   $59.25   $59.25   $59.30  
  Purchase #3 $166.32   6.400%   $176.9645   $176.96   $176.95   $177.00  
  Purchase #4 $129.48   9.152%   $141.33   $141.33   $141.35   $141.30  
  Purchase #5 $71.97   7.844%   $77.6153   $77.62   $77.60   $77.60  
  Purchase #6 $121.99   8.176%   $131.9639   $131.96   $131.95   $132.00  
  Purchase #7 $205.44   13.530%   $233.236   $233.24   $233.25   $233.20  
  7 purchase totals = $870.71       $955.2584   $955.26   $955.25   $955.30