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 $152.32   6.332%   $161.9649   $161.96   $161.95   $162.00  
  Purchase #2 $172.54   11.523%   $192.4218   $192.42   $192.40   $192.40  
  Purchase #3 $85.31   9.149%   $93.115   $93.12   $93.10   $93.10  
  Purchase #4 $232.82   4.459%   $243.2014   $243.20   $243.20   $243.20  
  Purchase #5 $65.77   11.563%   $73.375   $73.38   $73.40   $73.40  
  Purchase #6 $183.42   13.658%   $208.4715   $208.47   $208.45   $208.50  
  Purchase #7 $223.28   13.792%   $254.0748   $254.07   $254.05   $254.10  
  7 purchase totals = $1,115.46       $1,226.6244   $1,226.62   $1,226.55   $1,226.70