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 $107.97   6.127%   $114.5853   $114.59   $114.60   $114.60  
  Purchase #2 $59.58   8.412%   $64.5919   $64.59   $64.60   $64.60  
  Purchase #3 $88.86   6.502%   $94.6377   $94.64   $94.65   $94.60  
  Purchase #4 $19.52   9.843%   $21.4414   $21.44   $21.45   $21.40  
  Purchase #5 $201.60   11.189%   $224.157   $224.16   $224.15   $224.20  
  Purchase #6 $193.56   4.148%   $201.5889   $201.59   $201.60   $201.60  
  Purchase #7 $234.73   12.291%   $263.5807   $263.58   $263.60   $263.60  
  7 purchase totals = $905.82       $984.5829   $984.59   $984.65   $984.60