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 $247.87   8.661%   $269.338   $269.34   $269.35   $269.30  
  Purchase #2 $23.33   11.528%   $26.0195   $26.02   $26.00   $26.00  
  Purchase #3 $155.84   6.679%   $166.2486   $166.25   $166.25   $166.20  
  Purchase #4 $162.32   12.640%   $182.8372   $182.84   $182.85   $182.80  
  Purchase #5 $144.45   10.865%   $160.1445   $160.14   $160.15   $160.10  
  Purchase #6 $232.55   13.358%   $263.614   $263.61   $263.60   $263.60  
  Purchase #7 $50.71   3.184%   $52.3246   $52.32   $52.30   $52.30  
  7 purchase totals = $1,017.07       $1,120.5264   $1,120.52   $1,120.50   $1,120.30