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 $80.60   6.658%   $85.9663   $85.97   $85.95   $86.00  
  Purchase #2 $143.60   6.335%   $152.6971   $152.70   $152.70   $152.70  
  Purchase #3 $236.55   11.816%   $264.5007   $264.50   $264.50   $264.50  
  Purchase #4 $96.68   11.437%   $107.7373   $107.74   $107.75   $107.70  
  Purchase #5 $66.52   7.800%   $71.7086   $71.71   $71.70   $71.70  
  Purchase #6 $26.93   13.573%   $30.5852   $30.59   $30.60   $30.60  
  Purchase #7 $68.95   5.429%   $72.6933   $72.69   $72.70   $72.70  
  7 purchase totals = $719.83       $785.8885   $785.90   $785.90   $785.90