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 $161.73   13.276%   $183.2013   $183.20   $183.20   $183.20  
  Purchase #2 $123.69   12.183%   $138.7592   $138.76   $138.75   $138.80  
  Purchase #3 $27.60   12.280%   $30.9893   $30.99   $31.00   $31.00  
  Purchase #4 $47.98   9.498%   $52.5371   $52.54   $52.55   $52.50  
  Purchase #5 $199.69   3.406%   $206.4914   $206.49   $206.50   $206.50  
  Purchase #6 $28.82   13.842%   $32.8093   $32.81   $32.80   $32.80  
  Purchase #7 $111.70   4.465%   $116.6874   $116.69   $116.70   $116.70  
  7 purchase totals = $701.21       $761.4750   $761.48   $761.50   $761.50