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 $154.77   11.854%   $173.1164   $173.12   $173.10   $173.10  
  Purchase #2 $174.51   12.795%   $196.8386   $196.84   $196.85   $196.80  
  Purchase #3 $70.78   5.160%   $74.4322   $74.43   $74.45   $74.40  
  Purchase #4 $245.84   7.221%   $263.5921   $263.59   $263.60   $263.60  
  Purchase #5 $218.92   10.485%   $241.8738   $241.87   $241.85   $241.90  
  Purchase #6 $164.40   6.618%   $175.28   $175.28   $175.30   $175.30  
  Purchase #7 $70.36   12.616%   $79.2366   $79.24   $79.25   $79.20  
  7 purchase totals = $1,099.58       $1,204.3697   $1,204.37   $1,204.40   $1,204.30