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 $220.52   11.556%   $246.0033   $246.00   $246.00   $246.00  
  Purchase #2 $183.98   8.694%   $199.9752   $199.98   $200.00   $200.00  
  Purchase #3 $86.84   11.837%   $97.1193   $97.12   $97.10   $97.10  
  Purchase #4 $118.49   11.173%   $131.7289   $131.73   $131.75   $131.70  
  Purchase #5 $135.66   5.490%   $143.1077   $143.11   $143.10   $143.10  
  Purchase #6 $205.60   3.798%   $213.4087   $213.41   $213.40   $213.40  
  Purchase #7 $63.75   10.748%   $70.6019   $70.60   $70.60   $70.60  
  7 purchase totals = $1,014.84       $1,101.9450   $1,101.95   $1,101.95   $1,101.90