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 $248.38   9.400%   $271.7277   $271.73   $271.75   $271.70  
  Purchase #2 $112.45   6.511%   $119.7716   $119.77   $119.75   $119.80  
  Purchase #3 $77.45   4.641%   $81.0445   $81.04   $81.05   $81.00  
  Purchase #4 $214.77   4.727%   $224.9222   $224.92   $224.90   $224.90  
  Purchase #5 $197.37   3.149%   $203.5852   $203.59   $203.60   $203.60  
  Purchase #6 $226.89   4.325%   $236.703   $236.70   $236.70   $236.70  
  Purchase #7 $48.58   11.138%   $53.9908   $53.99   $54.00   $54.00  
  7 purchase totals = $1,125.89       $1,191.7450   $1,191.74   $1,191.75   $1,191.70