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 $184.89   10.794%   $204.847   $204.85   $204.85   $204.80  
  Purchase #2 $104.53   11.262%   $116.3022   $116.30   $116.30   $116.30  
  Purchase #3 $152.69   10.743%   $169.0935   $169.09   $169.10   $169.10  
  Purchase #4 $14.32   4.233%   $14.9262   $14.93   $14.95   $14.90  
  Purchase #5 $162.85   6.213%   $172.9679   $172.97   $172.95   $173.00  
  Purchase #6 $172.98   5.555%   $182.589   $182.59   $182.60   $182.60  
  Purchase #7 $44.44   12.651%   $50.0621   $50.06   $50.05   $50.10  
  7 purchase totals = $836.70       $910.7879   $910.79   $910.80   $910.80