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 $227.48   8.547%   $246.9227   $246.92   $246.90   $246.90  
  Purchase #2 $5.87   12.618%   $6.6107   $6.61   $6.60   $6.60  
  Purchase #3 $191.77   3.662%   $198.7926   $198.79   $198.80   $198.80  
  Purchase #4 $64.98   7.291%   $69.7177   $69.72   $69.70   $69.70  
  Purchase #5 $22.61   3.317%   $23.36   $23.36   $23.35   $23.40  
  Purchase #6 $87.55   3.738%   $90.8226   $90.82   $90.80   $90.80  
  Purchase #7 $58.50   8.408%   $63.4187   $63.42   $63.40   $63.40  
  7 purchase totals = $658.76       $699.6450   $699.64   $699.55   $699.60