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 $58.42   9.250%   $63.8239   $63.82   $63.80   $63.80  
  Purchase #2 $27.63   5.570%   $29.169   $29.17   $29.15   $29.20  
  Purchase #3 $96.53   9.331%   $105.5372   $105.54   $105.55   $105.50  
  Purchase #4 $181.59   11.236%   $201.9935   $201.99   $202.00   $202.00  
  Purchase #5 $244.88   13.266%   $277.3658   $277.37   $277.35   $277.40  
  Purchase #6 $31.41   9.861%   $34.5073   $34.51   $34.50   $34.50  
  Purchase #7 $111.95   3.291%   $115.6343   $115.63   $115.65   $115.60  
  7 purchase totals = $752.41       $828.0310   $828.03   $828.00   $828.00