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 $53.40   12.212%   $59.9212   $59.92   $59.90   $59.90  
  Purchase #2 $135.29   13.107%   $153.0225   $153.02   $153.00   $153.00  
  Purchase #3 $45.50   5.428%   $47.9697   $47.97   $47.95   $48.00  
  Purchase #4 $164.82   10.124%   $181.5064   $181.51   $181.50   $181.50  
  Purchase #5 $171.94   11.115%   $191.0511   $191.05   $191.05   $191.10  
  Purchase #6 $26.88   13.750%   $30.576   $30.58   $30.60   $30.60  
  Purchase #7 $53.92   11.681%   $60.2184   $60.22   $60.20   $60.20  
  7 purchase totals = $651.75       $724.2653   $724.27   $724.20   $724.30