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 $246.56   8.179%   $266.7261   $266.73   $266.75   $266.70  
  Purchase #2 $247.67   10.225%   $272.9943   $272.99   $273.00   $273.00  
  Purchase #3 $67.52   5.826%   $71.4537   $71.45   $71.45   $71.50  
  Purchase #4 $183.57   13.272%   $207.9334   $207.93   $207.95   $207.90  
  Purchase #5 $213.81   8.464%   $231.9069   $231.91   $231.90   $231.90  
  Purchase #6 $242.68   8.145%   $262.4463   $262.45   $262.45   $262.40  
  Purchase #7 $150.97   11.133%   $167.7775   $167.78   $167.80   $167.80  
  7 purchase totals = $1,352.78       $1,481.2382   $1,481.24   $1,481.30   $1,481.20