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 $66.47   13.723%   $75.5917   $75.59   $75.60   $75.60  
  Purchase #2 $166.96   10.758%   $184.9216   $184.92   $184.90   $184.90  
  Purchase #3 $196.88   11.623%   $219.7634   $219.76   $219.75   $219.80  
  Purchase #4 $145.74   8.161%   $157.6338   $157.63   $157.65   $157.60  
  Purchase #5 $190.82   12.156%   $214.0161   $214.02   $214.00   $214.00  
  Purchase #6 $193.92   9.862%   $213.0444   $213.04   $213.05   $213.00  
  Purchase #7 $189.68   6.236%   $201.5084   $201.51   $201.50   $201.50  
  7 purchase totals = $1,150.47       $1,266.4794   $1,266.47   $1,266.45   $1,266.40