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 $244.61   3.275%   $252.621   $252.62   $252.60   $252.60  
  Purchase #2 $33.85   3.718%   $35.1085   $35.11   $35.10   $35.10  
  Purchase #3 $226.41   7.533%   $243.4655   $243.47   $243.45   $243.50  
  Purchase #4 $203.27   3.863%   $211.1223   $211.12   $211.10   $211.10  
  Purchase #5 $136.44   6.836%   $145.767   $145.77   $145.75   $145.80  
  Purchase #6 $203.68   10.481%   $225.0277   $225.03   $225.05   $225.00  
  Purchase #7 $97.89   10.474%   $108.143   $108.14   $108.15   $108.10  
  7 purchase totals = $1,146.15       $1,221.2550   $1,221.26   $1,221.20   $1,221.20