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 $60.28   8.678%   $65.5111   $65.51   $65.50   $65.50  
  Purchase #2 $35.71   3.715%   $37.0366   $37.04   $37.05   $37.00  
  Purchase #3 $156.48   10.261%   $172.5364   $172.54   $172.55   $172.50  
  Purchase #4 $40.65   3.756%   $42.1768   $42.18   $42.20   $42.20  
  Purchase #5 $240.45   5.376%   $253.3766   $253.38   $253.40   $253.40  
  Purchase #6 $50.95   3.636%   $52.8025   $52.80   $52.80   $52.80  
  Purchase #7 $220.47   6.363%   $234.4985   $234.50   $234.50   $234.50  
  7 purchase totals = $804.99       $857.9385   $857.95   $858.00   $857.90