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 $24.84   7.270%   $26.6459   $26.65   $26.65   $26.60  
  Purchase #2 $138.63   10.799%   $153.6007   $153.60   $153.60   $153.60  
  Purchase #3 $65.91   7.522%   $70.8678   $70.87   $70.85   $70.90  
  Purchase #4 $177.84   9.191%   $194.1853   $194.19   $194.20   $194.20  
  Purchase #5 $100.81   13.586%   $114.506   $114.51   $114.50   $114.50  
  Purchase #6 $191.28   13.506%   $217.1143   $217.11   $217.10   $217.10  
  Purchase #7 $9.32   11.156%   $10.3597   $10.36   $10.35   $10.40  
  7 purchase totals = $708.63       $787.2797   $787.29   $787.25   $787.30