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 $58.46   6.709%   $62.3821   $62.38   $62.40   $62.40  
  Purchase #2 $8.97   7.434%   $9.6368   $9.64   $9.65   $9.60  
  Purchase #3 $172.59   5.595%   $182.2464   $182.25   $182.25   $182.20  
  Purchase #4 $80.65   8.599%   $87.5851   $87.59   $87.60   $87.60  
  Purchase #5 $5.85   11.491%   $6.5222   $6.52   $6.50   $6.50  
  Purchase #6 $171.75   4.637%   $179.714   $179.71   $179.70   $179.70  
  Purchase #7 $240.32   7.133%   $257.462   $257.46   $257.45   $257.50  
  7 purchase totals = $738.59       $785.5486   $785.55   $785.55   $785.50