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 $72.49   11.137%   $80.5632   $80.56   $80.55   $80.60  
  Purchase #2 $193.28   8.465%   $209.6412   $209.64   $209.65   $209.60  
  Purchase #3 $148.46   13.736%   $168.8525   $168.85   $168.85   $168.90  
  Purchase #4 $184.72   12.679%   $208.1406   $208.14   $208.15   $208.10  
  Purchase #5 $239.58   11.446%   $267.0023   $267.00   $267.00   $267.00  
  Purchase #6 $160.87   9.518%   $176.1816   $176.18   $176.20   $176.20  
  Purchase #7 $75.71   8.132%   $81.8667   $81.87   $81.85   $81.90  
  7 purchase totals = $1,075.11       $1,192.2481   $1,192.24   $1,192.25   $1,192.30