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 $162.63   10.592%   $179.8558   $179.86   $179.85   $179.90  
  Purchase #2 $69.69   9.326%   $76.1893   $76.19   $76.20   $76.20  
  Purchase #3 $77.28   9.750%   $84.8148   $84.81   $84.80   $84.80  
  Purchase #4 $238.90   6.547%   $254.5408   $254.54   $254.55   $254.50  
  Purchase #5 $215.43   13.782%   $245.1206   $245.12   $245.10   $245.10  
  Purchase #6 $243.61   8.427%   $264.139   $264.14   $264.15   $264.10  
  Purchase #7 $12.57   12.800%   $14.179   $14.18   $14.20   $14.20  
  7 purchase totals = $1,020.11       $1,118.8393   $1,118.84   $1,118.85   $1,118.80