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 $33.46   6.629%   $35.6781   $35.68   $35.70   $35.70  
  Purchase #2 $200.91   6.780%   $214.5317   $214.53   $214.55   $214.50  
  Purchase #3 $153.35   4.761%   $160.651   $160.65   $160.65   $160.70  
  Purchase #4 $80.40   9.454%   $88.001   $88.00   $88.00   $88.00  
  Purchase #5 $176.63   6.162%   $187.5139   $187.51   $187.50   $187.50  
  Purchase #6 $99.74   13.525%   $113.2298   $113.23   $113.25   $113.20  
  Purchase #7 $141.55   11.398%   $157.6839   $157.68   $157.70   $157.70  
  7 purchase totals = $886.04       $957.2894   $957.28   $957.35   $957.30