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 $236.94   12.370%   $266.2495   $266.25   $266.25   $266.20  
  Purchase #2 $79.48   6.620%   $84.7416   $84.74   $84.75   $84.70  
  Purchase #3 $24.75   7.133%   $26.5154   $26.52   $26.50   $26.50  
  Purchase #4 $117.44   7.521%   $126.2727   $126.27   $126.25   $126.30  
  Purchase #5 $63.75   3.400%   $65.9175   $65.92   $65.90   $65.90  
  Purchase #6 $202.29   10.781%   $224.0989   $224.10   $224.10   $224.10  
  Purchase #7 $231.46   8.768%   $251.7544   $251.75   $251.75   $251.80  
  7 purchase totals = $956.11       $1,045.5500   $1,045.55   $1,045.50   $1,045.50