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 $193.79   13.349%   $219.659   $219.66   $219.65   $219.70  
  Purchase #2 $228.33   8.507%   $247.754   $247.75   $247.75   $247.80  
  Purchase #3 $37.80   13.464%   $42.8894   $42.89   $42.90   $42.90  
  Purchase #4 $24.31   7.773%   $26.1996   $26.20   $26.20   $26.20  
  Purchase #5 $175.83   5.520%   $185.5358   $185.54   $185.55   $185.50  
  Purchase #6 $236.99   3.401%   $245.05   $245.05   $245.05   $245.10  
  Purchase #7 $62.67   3.689%   $64.9819   $64.98   $65.00   $65.00  
  7 purchase totals = $959.72       $1,032.0697   $1,032.07   $1,032.10   $1,032.20