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 $69.49   11.699%   $77.6196   $77.62   $77.60   $77.60  
  Purchase #2 $230.86   7.358%   $247.8467   $247.85   $247.85   $247.80  
  Purchase #3 $17.36   7.805%   $18.7149   $18.71   $18.70   $18.70  
  Purchase #4 $183.62   12.705%   $206.9489   $206.95   $206.95   $206.90  
  Purchase #5 $203.87   9.202%   $222.6301   $222.63   $222.65   $222.60  
  Purchase #6 $98.71   7.456%   $106.0698   $106.07   $106.05   $106.10  
  Purchase #7 $221.84   3.112%   $228.7437   $228.74   $228.75   $228.70  
  7 purchase totals = $1,025.75       $1,108.5737   $1,108.57   $1,108.55   $1,108.40