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 $173.29   13.151%   $196.0794   $196.08   $196.10   $196.10  
  Purchase #2 $247.93   3.153%   $255.7472   $255.75   $255.75   $255.70  
  Purchase #3 $170.57   9.372%   $186.5558   $186.56   $186.55   $186.60  
  Purchase #4 $20.77   10.596%   $22.9708   $22.97   $22.95   $23.00  
  Purchase #5 $68.63   6.689%   $73.2207   $73.22   $73.20   $73.20  
  Purchase #6 $159.85   12.279%   $179.478   $179.48   $179.50   $179.50  
  Purchase #7 $222.64   11.516%   $248.2792   $248.28   $248.30   $248.30  
  7 purchase totals = $1,063.68       $1,162.3311   $1,162.34   $1,162.35   $1,162.40