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 $92.61   8.547%   $100.5254   $100.53   $100.55   $100.50  
  Purchase #2 $196.62   11.559%   $219.3473   $219.35   $219.35   $219.30  
  Purchase #3 $139.66   7.307%   $149.865   $149.87   $149.85   $149.90  
  Purchase #4 $26.68   10.438%   $29.4649   $29.46   $29.45   $29.50  
  Purchase #5 $33.43   10.808%   $37.0431   $37.04   $37.05   $37.00  
  Purchase #6 $199.63   5.641%   $210.8911   $210.89   $210.90   $210.90  
  Purchase #7 $215.43   6.811%   $230.1029   $230.10   $230.10   $230.10  
  7 purchase totals = $904.06       $977.2397   $977.24   $977.25   $977.20