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 $167.39   11.584%   $186.7805   $186.78   $186.80   $186.80  
  Purchase #2 $98.78   8.631%   $107.3057   $107.31   $107.30   $107.30  
  Purchase #3 $33.56   7.779%   $36.1706   $36.17   $36.15   $36.20  
  Purchase #4 $76.97   8.604%   $83.5925   $83.59   $83.60   $83.60  
  Purchase #5 $207.33   6.522%   $220.8521   $220.85   $220.85   $220.90  
  Purchase #6 $57.73   6.784%   $61.6464   $61.65   $61.65   $61.60  
  Purchase #7 $128.46   9.205%   $140.2847   $140.28   $140.30   $140.30  
  7 purchase totals = $770.22       $836.6325   $836.63   $836.65   $836.70