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 $87.27   7.771%   $94.0518   $94.05   $94.05   $94.10  
  Purchase #2 $26.59   12.561%   $29.93   $29.93   $29.95   $29.90  
  Purchase #3 $69.46   5.417%   $73.2226   $73.22   $73.20   $73.20  
  Purchase #4 $185.33   9.389%   $202.7306   $202.73   $202.75   $202.70  
  Purchase #5 $161.91   8.492%   $175.6594   $175.66   $175.65   $175.70  
  Purchase #6 $151.40   12.542%   $170.3886   $170.39   $170.40   $170.40  
  Purchase #7 $13.85   7.459%   $14.8831   $14.88   $14.90   $14.90  
  7 purchase totals = $695.81       $760.8661   $760.86   $760.90   $760.90