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 $81.36   3.568%   $84.2629   $84.26   $84.25   $84.30  
  Purchase #2 $53.79   12.818%   $60.6848   $60.68   $60.70   $60.70  
  Purchase #3 $212.49   5.272%   $223.6925   $223.69   $223.70   $223.70  
  Purchase #4 $91.31   11.715%   $102.007   $102.01   $102.00   $102.00  
  Purchase #5 $96.55   13.323%   $109.4134   $109.41   $109.40   $109.40  
  Purchase #6 $195.25   4.291%   $203.6282   $203.63   $203.65   $203.60  
  Purchase #7 $17.26   4.305%   $18.003   $18.00   $18.00   $18.00  
  7 purchase totals = $748.01       $801.6918   $801.68   $801.70   $801.70