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 $89.61   6.858%   $95.7555   $95.76   $95.75   $95.80  
  Purchase #2 $77.32   3.286%   $79.8607   $79.86   $79.85   $79.90  
  Purchase #3 $33.26   4.435%   $34.7351   $34.74   $34.75   $34.70  
  Purchase #4 $233.86   8.273%   $253.2072   $253.21   $253.20   $253.20  
  Purchase #5 $75.85   9.310%   $82.9116   $82.91   $82.90   $82.90  
  Purchase #6 $49.28   11.688%   $55.0398   $55.04   $55.05   $55.00  
  Purchase #7 $140.95   4.732%   $147.6198   $147.62   $147.60   $147.60  
  7 purchase totals = $700.13       $749.1297   $749.14   $749.10   $749.10