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 $248.91   13.536%   $282.6025   $282.60   $282.60   $282.60  
  Purchase #2 $152.58   8.509%   $165.563   $165.56   $165.55   $165.60  
  Purchase #3 $182.98   11.495%   $204.0136   $204.01   $204.00   $204.00  
  Purchase #4 $199.95   13.399%   $226.7413   $226.74   $226.75   $226.70  
  Purchase #5 $24.70   4.221%   $25.7426   $25.74   $25.75   $25.70  
  Purchase #6 $98.71   13.475%   $112.0112   $112.01   $112.00   $112.00  
  Purchase #7 $36.64   6.288%   $38.9439   $38.94   $38.95   $38.90  
  7 purchase totals = $944.47       $1,055.6181   $1,055.60   $1,055.60   $1,055.50