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 $31.26   11.847%   $34.9634   $34.96   $34.95   $35.00  
  Purchase #2 $232.99   13.739%   $265.0005   $265.00   $265.00   $265.00  
  Purchase #3 $53.94   10.379%   $59.5384   $59.54   $59.55   $59.50  
  Purchase #4 $154.99   3.715%   $160.7479   $160.75   $160.75   $160.70  
  Purchase #5 $15.72   11.678%   $17.5558   $17.56   $17.55   $17.60  
  Purchase #6 $37.27   4.477%   $38.9386   $38.94   $38.95   $38.90  
  Purchase #7 $202.70   7.643%   $218.1924   $218.19   $218.20   $218.20  
  7 purchase totals = $728.87       $794.9370   $794.94   $794.95   $794.90