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 $198.57   4.652%   $207.8075   $207.81   $207.80   $207.80  
  Purchase #2 $85.26   10.596%   $94.2941   $94.29   $94.30   $94.30  
  Purchase #3 $118.94   6.133%   $126.2346   $126.23   $126.25   $126.20  
  Purchase #4 $247.86   6.727%   $264.5335   $264.53   $264.55   $264.50  
  Purchase #5 $226.75   11.711%   $253.3047   $253.30   $253.30   $253.30  
  Purchase #6 $37.30   6.407%   $39.6898   $39.69   $39.70   $39.70  
  Purchase #7 $18.99   12.502%   $21.3641   $21.36   $21.35   $21.40  
  7 purchase totals = $933.67       $1,007.2283   $1,007.21   $1,007.25   $1,007.20