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 $216.53   12.376%   $243.3278   $243.33   $243.35   $243.30  
  Purchase #2 $182.50   3.405%   $188.7141   $188.71   $188.70   $188.70  
  Purchase #3 $70.94   5.157%   $74.5984   $74.60   $74.60   $74.60  
  Purchase #4 $24.80   6.755%   $26.4752   $26.48   $26.50   $26.50  
  Purchase #5 $122.98   10.851%   $136.3246   $136.32   $136.30   $136.30  
  Purchase #6 $29.88   8.128%   $32.3086   $32.31   $32.30   $32.30  
  Purchase #7 $53.58   8.713%   $58.2484   $58.25   $58.25   $58.20  
  7 purchase totals = $701.21       $759.9971   $760.00   $760.00   $759.90