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 $62.61   13.595%   $71.1218   $71.12   $71.10   $71.10  
  Purchase #2 $232.55   8.168%   $251.5447   $251.54   $251.55   $251.50  
  Purchase #3 $232.73   7.690%   $250.6269   $250.63   $250.65   $250.60  
  Purchase #4 $58.93   3.841%   $61.1935   $61.19   $61.20   $61.20  
  Purchase #5 $72.84   10.492%   $80.4824   $80.48   $80.50   $80.50  
  Purchase #6 $49.50   12.417%   $55.6464   $55.65   $55.65   $55.60  
  Purchase #7 $224.99   3.156%   $232.0907   $232.09   $232.10   $232.10  
  7 purchase totals = $934.15       $1,002.7064   $1,002.70   $1,002.75   $1,002.60