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 $136.99   10.659%   $151.5918   $151.59   $151.60   $151.60  
  Purchase #2 $94.58   6.445%   $100.6757   $100.68   $100.70   $100.70  
  Purchase #3 $120.61   10.160%   $132.864   $132.86   $132.85   $132.90  
  Purchase #4 $52.87   8.667%   $57.4522   $57.45   $57.45   $57.50  
  Purchase #5 $217.44   4.253%   $226.6877   $226.69   $226.70   $226.70  
  Purchase #6 $23.42   11.785%   $26.18   $26.18   $26.20   $26.20  
  Purchase #7 $199.28   3.123%   $205.5035   $205.50   $205.50   $205.50  
  7 purchase totals = $845.19       $900.9549   $900.95   $901.00   $901.10