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 $250.56   5.841%   $265.1952   $265.20   $265.20   $265.20  
  Purchase #2 $151.54   7.806%   $163.3692   $163.37   $163.35   $163.40  
  Purchase #3 $185.94   5.271%   $195.7409   $195.74   $195.75   $195.70  
  Purchase #4 $86.79   3.650%   $89.9578   $89.96   $89.95   $90.00  
  Purchase #5 $225.84   6.231%   $239.9121   $239.91   $239.90   $239.90  
  Purchase #6 $181.97   12.393%   $204.5215   $204.52   $204.50   $204.50  
  Purchase #7 $81.34   8.673%   $88.3946   $88.39   $88.40   $88.40  
  7 purchase totals = $1,163.98       $1,247.0913   $1,247.09   $1,247.05   $1,247.10