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 $226.78   7.553%   $243.9087   $243.91   $243.90   $243.90  
  Purchase #2 $212.90   9.377%   $232.8636   $232.86   $232.85   $232.90  
  Purchase #3 $172.62   11.642%   $192.7164   $192.72   $192.70   $192.70  
  Purchase #4 $224.55   13.379%   $254.5925   $254.59   $254.60   $254.60  
  Purchase #5 $133.35   11.316%   $148.4399   $148.44   $148.45   $148.40  
  Purchase #6 $239.32   11.250%   $266.2435   $266.24   $266.25   $266.20  
  Purchase #7 $133.75   8.416%   $145.0064   $145.01   $145.00   $145.00  
  7 purchase totals = $1,343.27       $1,483.7710   $1,483.77   $1,483.75   $1,483.70