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 $21.95   8.251%   $23.7611   $23.76   $23.75   $23.80  
  Purchase #2 $191.87   6.318%   $203.9923   $203.99   $204.00   $204.00  
  Purchase #3 $229.48   9.224%   $250.6472   $250.65   $250.65   $250.60  
  Purchase #4 $53.62   13.781%   $61.0094   $61.01   $61.00   $61.00  
  Purchase #5 $189.37   3.346%   $195.7063   $195.71   $195.70   $195.70  
  Purchase #6 $38.80   6.362%   $41.2685   $41.27   $41.25   $41.30  
  Purchase #7 $230.70   8.808%   $251.0201   $251.02   $251.00   $251.00  
  7 purchase totals = $955.79       $1,027.4049   $1,027.41   $1,027.35   $1,027.40