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 $205.49   10.874%   $227.835   $227.84   $227.85   $227.80  
  Purchase #2 $194.57   3.551%   $201.4792   $201.48   $201.50   $201.50  
  Purchase #3 $165.83   5.866%   $175.5576   $175.56   $175.55   $175.60  
  Purchase #4 $77.64   5.767%   $82.1175   $82.12   $82.10   $82.10  
  Purchase #5 $218.97   3.167%   $225.9048   $225.90   $225.90   $225.90  
  Purchase #6 $121.55   10.213%   $133.9639   $133.96   $133.95   $134.00  
  Purchase #7 $14.49   5.807%   $15.3314   $15.33   $15.35   $15.30  
  7 purchase totals = $998.54       $1,062.1894   $1,062.19   $1,062.20   $1,062.20