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 $206.60   11.334%   $230.016   $230.02   $230.00   $230.00  
  Purchase #2 $159.97   12.291%   $179.6319   $179.63   $179.65   $179.60  
  Purchase #3 $106.43   6.670%   $113.5289   $113.53   $113.55   $113.50  
  Purchase #4 $49.63   12.677%   $55.9216   $55.92   $55.90   $55.90  
  Purchase #5 $34.29   3.802%   $35.5937   $35.59   $35.60   $35.60  
  Purchase #6 $241.77   12.820%   $272.7649   $272.76   $272.75   $272.80  
  Purchase #7 $154.53   3.686%   $160.226   $160.23   $160.25   $160.20  
  7 purchase totals = $953.22       $1,047.6830   $1,047.68   $1,047.70   $1,047.60