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 $234.92   11.624%   $262.2271   $262.23   $262.25   $262.20  
  Purchase #2 $84.94   7.389%   $91.2162   $91.22   $91.20   $91.20  
  Purchase #3 $35.97   6.687%   $38.3753   $38.38   $38.40   $38.40  
  Purchase #4 $227.87   6.122%   $241.8202   $241.82   $241.80   $241.80  
  Purchase #5 $95.77   3.325%   $98.9544   $98.95   $98.95   $99.00  
  Purchase #6 $180.67   12.561%   $203.364   $203.36   $203.35   $203.40  
  Purchase #7 $106.67   8.402%   $115.6324   $115.63   $115.65   $115.60  
  7 purchase totals = $966.81       $1,051.5896   $1,051.59   $1,051.60   $1,051.60