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 $51.25   9.608%   $56.1741   $56.17   $56.15   $56.20  
  Purchase #2 $215.25   10.311%   $237.4444   $237.44   $237.45   $237.40  
  Purchase #3 $151.73   11.376%   $168.9908   $168.99   $169.00   $169.00  
  Purchase #4 $156.59   7.508%   $168.3468   $168.35   $168.35   $168.30  
  Purchase #5 $218.87   6.536%   $233.1753   $233.18   $233.20   $233.20  
  Purchase #6 $204.48   7.419%   $219.6504   $219.65   $219.65   $219.70  
  Purchase #7 $104.27   6.174%   $110.7076   $110.71   $110.70   $110.70  
  7 purchase totals = $1,102.44       $1,194.4894   $1,194.49   $1,194.50   $1,194.50