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 $235.71   11.194%   $262.0954   $262.10   $262.10   $262.10  
  Purchase #2 $202.75   11.807%   $226.6887   $226.69   $226.70   $226.70  
  Purchase #3 $196.71   9.688%   $215.7673   $215.77   $215.75   $215.80  
  Purchase #4 $53.72   12.745%   $60.5666   $60.57   $60.55   $60.60  
  Purchase #5 $206.87   6.204%   $219.7042   $219.70   $219.70   $219.70  
  Purchase #6 $44.87   12.438%   $50.4509   $50.45   $50.45   $50.50  
  Purchase #7 $226.76   7.572%   $243.9303   $243.93   $243.95   $243.90  
  7 purchase totals = $1,167.39       $1,279.2034   $1,279.21   $1,279.20   $1,279.30