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 $34.98   5.851%   $37.0267   $37.03   $37.05   $37.00  
  Purchase #2 $130.37   9.402%   $142.6274   $142.63   $142.65   $142.60  
  Purchase #3 $27.89   11.117%   $30.9905   $30.99   $31.00   $31.00  
  Purchase #4 $224.71   8.404%   $243.5946   $243.59   $243.60   $243.60  
  Purchase #5 $182.44   11.571%   $203.5501   $203.55   $203.55   $203.60  
  Purchase #6 $137.29   10.420%   $151.5956   $151.60   $151.60   $151.60  
  Purchase #7 $122.33   9.341%   $133.7568   $133.76   $133.75   $133.80  
  7 purchase totals = $860.01       $943.1417   $943.15   $943.20   $943.20