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 $249.51   10.620%   $276.008   $276.01   $276.00   $276.00  
  Purchase #2 $240.53   3.617%   $249.23   $249.23   $249.25   $249.20  
  Purchase #3 $210.98   7.300%   $226.3815   $226.38   $226.40   $226.40  
  Purchase #4 $191.59   11.843%   $214.28   $214.28   $214.30   $214.30  
  Purchase #5 $204.75   12.466%   $230.2741   $230.27   $230.25   $230.30  
  Purchase #6 $219.53   3.445%   $227.0928   $227.09   $227.10   $227.10  
  Purchase #7 $175.37   7.603%   $188.7034   $188.70   $188.70   $188.70  
  7 purchase totals = $1,492.26       $1,611.9698   $1,611.96   $1,612.00   $1,612.00