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 $59.76   11.696%   $66.7495   $66.75   $66.75   $66.70  
  Purchase #2 $192.53   5.484%   $203.0883   $203.09   $203.10   $203.10  
  Purchase #3 $185.99   3.561%   $192.6131   $192.61   $192.60   $192.60  
  Purchase #4 $54.85   13.235%   $62.1094   $62.11   $62.10   $62.10  
  Purchase #5 $182.50   8.505%   $198.0216   $198.02   $198.00   $198.00  
  Purchase #6 $121.72   3.727%   $126.2565   $126.26   $126.25   $126.30  
  Purchase #7 $208.77   7.780%   $225.0123   $225.01   $225.00   $225.00  
  7 purchase totals = $1,006.12       $1,073.8507   $1,073.85   $1,073.80   $1,073.80