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 $202.79   11.241%   $225.5856   $225.59   $225.60   $225.60  
  Purchase #2 $49.55   5.327%   $52.1895   $52.19   $52.20   $52.20  
  Purchase #3 $243.86   12.647%   $274.701   $274.70   $274.70   $274.70  
  Purchase #4 $175.55   11.394%   $195.5522   $195.55   $195.55   $195.60  
  Purchase #5 $214.48   9.466%   $234.7827   $234.78   $234.80   $234.80  
  Purchase #6 $187.90   13.844%   $213.9129   $213.91   $213.90   $213.90  
  Purchase #7 $141.44   12.505%   $159.1271   $159.13   $159.15   $159.10  
  7 purchase totals = $1,215.57       $1,355.8510   $1,355.85   $1,355.90   $1,355.90