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 $122.75   3.378%   $126.8965   $126.90   $126.90   $126.90  
  Purchase #2 $229.52   11.173%   $255.1643   $255.16   $255.15   $255.20  
  Purchase #3 $215.95   12.679%   $243.3303   $243.33   $243.35   $243.30  
  Purchase #4 $249.38   12.708%   $281.0712   $281.07   $281.05   $281.10  
  Purchase #5 $241.88   3.869%   $251.2383   $251.24   $251.25   $251.20  
  Purchase #6 $68.74   11.326%   $76.5255   $76.53   $76.55   $76.50  
  Purchase #7 $64.54   5.690%   $68.2123   $68.21   $68.20   $68.20  
  7 purchase totals = $1,192.76       $1,302.4384   $1,302.44   $1,302.45   $1,302.40