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 $51.68   9.713%   $56.6997   $56.70   $56.70   $56.70  
  Purchase #2 $113.31   13.794%   $128.94   $128.94   $128.95   $128.90  
  Purchase #3 $111.49   3.200%   $115.0577   $115.06   $115.05   $115.10  
  Purchase #4 $218.43   10.365%   $241.0703   $241.07   $241.05   $241.10  
  Purchase #5 $194.77   4.727%   $203.9768   $203.98   $204.00   $204.00  
  Purchase #6 $156.40   5.843%   $165.5385   $165.54   $165.55   $165.50  
  Purchase #7 $235.63   5.543%   $248.691   $248.69   $248.70   $248.70  
  7 purchase totals = $1,081.71       $1,159.9740   $1,159.98   $1,160.00   $1,160.00