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 $170.32   8.481%   $184.7648   $184.76   $184.75   $184.80  
  Purchase #2 $71.83   6.298%   $76.3539   $76.35   $76.35   $76.40  
  Purchase #3 $207.52   5.164%   $218.2363   $218.24   $218.25   $218.20  
  Purchase #4 $16.34   4.631%   $17.0967   $17.10   $17.10   $17.10  
  Purchase #5 $226.27   6.550%   $241.0907   $241.09   $241.10   $241.10  
  Purchase #6 $239.35   11.341%   $266.4947   $266.49   $266.50   $266.50  
  Purchase #7 $119.30   6.504%   $127.0593   $127.06   $127.05   $127.10  
  7 purchase totals = $1,050.93       $1,131.0964   $1,131.09   $1,131.10   $1,131.20