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 $207.37   13.186%   $234.7138   $234.71   $234.70   $234.70  
  Purchase #2 $21.70   13.267%   $24.5789   $24.58   $24.60   $24.60  
  Purchase #3 $191.84   11.681%   $214.2488   $214.25   $214.25   $214.20  
  Purchase #4 $60.73   4.681%   $63.5728   $63.57   $63.55   $63.60  
  Purchase #5 $52.40   6.837%   $55.9826   $55.98   $56.00   $56.00  
  Purchase #6 $119.33   5.268%   $125.6163   $125.62   $125.60   $125.60  
  Purchase #7 $134.51   11.467%   $149.9343   $149.93   $149.95   $149.90  
  7 purchase totals = $787.88       $868.6475   $868.64   $868.65   $868.60