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 $162.94   6.422%   $173.404   $173.40   $173.40   $173.40  
  Purchase #2 $185.41   12.173%   $207.98   $207.98   $208.00   $208.00  
  Purchase #3 $220.86   9.295%   $241.3889   $241.39   $241.40   $241.40  
  Purchase #4 $156.32   11.573%   $174.4109   $174.41   $174.40   $174.40  
  Purchase #5 $51.54   13.179%   $58.3325   $58.33   $58.35   $58.30  
  Purchase #6 $148.37   9.623%   $162.6476   $162.65   $162.65   $162.60  
  Purchase #7 $237.82   6.580%   $253.4686   $253.47   $253.45   $253.50  
  7 purchase totals = $1,163.26       $1,271.6325   $1,271.63   $1,271.65   $1,271.60