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 $31.67   12.154%   $35.5192   $35.52   $35.50   $35.50  
  Purchase #2 $31.63   7.363%   $33.9589   $33.96   $33.95   $34.00  
  Purchase #3 $156.85   5.134%   $164.9027   $164.90   $164.90   $164.90  
  Purchase #4 $224.57   11.533%   $250.4697   $250.47   $250.45   $250.50  
  Purchase #5 $74.63   6.691%   $79.6235   $79.62   $79.60   $79.60  
  Purchase #6 $157.33   11.865%   $175.9972   $176.00   $176.00   $176.00  
  Purchase #7 $114.66   5.492%   $120.9571   $120.96   $120.95   $121.00  
  7 purchase totals = $791.34       $861.4283   $861.43   $861.35   $861.50