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 $239.46   5.513%   $252.6614   $252.66   $252.65   $252.70  
  Purchase #2 $8.58   4.213%   $8.9415   $8.94   $8.95   $8.90  
  Purchase #3 $58.98   6.296%   $62.6934   $62.69   $62.70   $62.70  
  Purchase #4 $53.50   10.808%   $59.2823   $59.28   $59.30   $59.30  
  Purchase #5 $156.52   8.846%   $170.3658   $170.37   $170.35   $170.40  
  Purchase #6 $125.25   10.634%   $138.5691   $138.57   $138.55   $138.60  
  Purchase #7 $64.72   8.841%   $70.4419   $70.44   $70.45   $70.40  
  7 purchase totals = $707.01       $762.9554   $762.95   $762.95   $763.00