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 $44.91   13.662%   $51.0456   $51.05   $51.05   $51.00  
  Purchase #2 $174.29   4.411%   $181.9779   $181.98   $182.00   $182.00  
  Purchase #3 $226.42   13.309%   $256.5542   $256.55   $256.55   $256.60  
  Purchase #4 $226.67   5.394%   $238.8966   $238.90   $238.90   $238.90  
  Purchase #5 $75.82   11.391%   $84.4567   $84.46   $84.45   $84.50  
  Purchase #6 $151.75   5.326%   $159.8322   $159.83   $159.85   $159.80  
  Purchase #7 $65.41   12.842%   $73.81   $73.81   $73.80   $73.80  
  7 purchase totals = $965.27       $1,046.5732   $1,046.58   $1,046.60   $1,046.60