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 $136.34   11.260%   $151.6919   $151.69   $151.70   $151.70  
  Purchase #2 $185.44   13.540%   $210.5486   $210.55   $210.55   $210.50  
  Purchase #3 $223.67   3.572%   $231.6595   $231.66   $231.65   $231.70  
  Purchase #4 $234.27   8.821%   $254.935   $254.94   $254.95   $254.90  
  Purchase #5 $197.83   13.158%   $223.8605   $223.86   $223.85   $223.90  
  Purchase #6 $211.39   3.431%   $218.6428   $218.64   $218.65   $218.60  
  Purchase #7 $58.37   4.344%   $60.9056   $60.91   $60.90   $60.90  
  7 purchase totals = $1,247.31       $1,352.2439   $1,352.25   $1,352.25   $1,352.20