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 $9.93   13.702%   $11.2906   $11.29   $11.30   $11.30  
  Purchase #2 $196.53   3.839%   $204.0748   $204.07   $204.05   $204.10  
  Purchase #3 $242.61   3.782%   $251.7855   $251.79   $251.80   $251.80  
  Purchase #4 $203.70   10.596%   $225.2841   $225.28   $225.30   $225.30  
  Purchase #5 $155.35   13.218%   $175.8842   $175.88   $175.90   $175.90  
  Purchase #6 $69.87   6.193%   $74.197   $74.20   $74.20   $74.20  
  Purchase #7 $203.27   13.219%   $230.1403   $230.14   $230.15   $230.10  
  7 purchase totals = $1,081.26       $1,172.6565   $1,172.65   $1,172.70   $1,172.70