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 $216.54   5.167%   $227.7286   $227.73   $227.75   $227.70  
  Purchase #2 $93.73   12.624%   $105.5625   $105.56   $105.55   $105.60  
  Purchase #3 $193.46   9.363%   $211.5737   $211.57   $211.55   $211.60  
  Purchase #4 $92.70   3.634%   $96.0687   $96.07   $96.05   $96.10  
  Purchase #5 $12.69   9.809%   $13.9348   $13.93   $13.95   $13.90  
  Purchase #6 $246.26   9.585%   $269.864   $269.86   $269.85   $269.90  
  Purchase #7 $187.77   5.696%   $198.4654   $198.47   $198.45   $198.50  
  7 purchase totals = $1,043.15       $1,123.1977   $1,123.19   $1,123.15   $1,123.30