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 $33.82   3.690%   $35.068   $35.07   $35.05   $35.10  
  Purchase #2 $164.98   3.675%   $171.043   $171.04   $171.05   $171.00  
  Purchase #3 $240.75   6.328%   $255.9847   $255.98   $256.00   $256.00  
  Purchase #4 $58.95   3.149%   $60.8063   $60.81   $60.80   $60.80  
  Purchase #5 $106.94   3.288%   $110.4562   $110.46   $110.45   $110.50  
  Purchase #6 $166.35   12.761%   $187.5779   $187.58   $187.60   $187.60  
  Purchase #7 $45.74   4.756%   $47.9154   $47.92   $47.90   $47.90  
  7 purchase totals = $817.53       $868.8515   $868.86   $868.85   $868.90