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 $60.38   11.433%   $67.2832   $67.28   $67.30   $67.30  
  Purchase #2 $230.59   9.206%   $251.8181   $251.82   $251.80   $251.80  
  Purchase #3 $244.84   8.833%   $266.4667   $266.47   $266.45   $266.50  
  Purchase #4 $37.58   11.518%   $41.9085   $41.91   $41.90   $41.90  
  Purchase #5 $204.74   10.226%   $225.6767   $225.68   $225.70   $225.70  
  Purchase #6 $212.25   12.302%   $238.361   $238.36   $238.35   $238.40  
  Purchase #7 $31.56   5.244%   $33.215   $33.22   $33.20   $33.20  
  7 purchase totals = $1,021.94       $1,124.7292   $1,124.74   $1,124.70   $1,124.80