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 $77.44   13.106%   $87.5893   $87.59   $87.60   $87.60  
  Purchase #2 $134.95   13.454%   $153.1062   $153.11   $153.10   $153.10  
  Purchase #3 $118.47   8.258%   $128.2533   $128.25   $128.25   $128.30  
  Purchase #4 $59.55   7.562%   $64.0532   $64.05   $64.05   $64.10  
  Purchase #5 $249.92   7.633%   $268.9964   $269.00   $269.00   $269.00  
  Purchase #6 $96.69   6.150%   $102.6364   $102.64   $102.65   $102.60  
  Purchase #7 $26.62   6.746%   $28.4158   $28.42   $28.40   $28.40  
  7 purchase totals = $763.64       $833.0506   $833.06   $833.05   $833.10