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 $60.25   12.841%   $67.9867   $67.99   $68.00   $68.00  
  Purchase #2 $111.32   11.354%   $123.9593   $123.96   $123.95   $124.00  
  Purchase #3 $153.92   13.380%   $174.5145   $174.51   $174.50   $174.50  
  Purchase #4 $19.90   9.240%   $21.7388   $21.74   $21.75   $21.70  
  Purchase #5 $172.86   6.540%   $184.165   $184.17   $184.15   $184.20  
  Purchase #6 $249.30   13.332%   $282.5367   $282.54   $282.55   $282.50  
  Purchase #7 $164.66   4.500%   $172.0697   $172.07   $172.05   $172.10  
  7 purchase totals = $932.21       $1,026.9707   $1,026.98   $1,026.95   $1,027.00