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 $161.64   3.122%   $166.6864   $166.69   $166.70   $166.70  
  Purchase #2 $188.84   7.674%   $203.3316   $203.33   $203.35   $203.30  
  Purchase #3 $74.68   11.170%   $83.0218   $83.02   $83.00   $83.00  
  Purchase #4 $32.42   4.120%   $33.7557   $33.76   $33.75   $33.80  
  Purchase #5 $30.53   9.676%   $33.4841   $33.48   $33.50   $33.50  
  Purchase #6 $208.40   11.566%   $232.5035   $232.50   $232.50   $232.50  
  Purchase #7 $154.36   8.343%   $167.2383   $167.24   $167.25   $167.20  
  7 purchase totals = $850.87       $920.0214   $920.02   $920.05   $920.00