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 $174.98   6.459%   $186.282   $186.28   $186.30   $186.30  
  Purchase #2 $47.70   7.104%   $51.0886   $51.09   $51.10   $51.10  
  Purchase #3 $209.74   6.556%   $223.4906   $223.49   $223.50   $223.50  
  Purchase #4 $34.87   13.216%   $39.4784   $39.48   $39.50   $39.50  
  Purchase #5 $165.92   8.405%   $179.8656   $179.87   $179.85   $179.90  
  Purchase #6 $219.87   6.295%   $233.7108   $233.71   $233.70   $233.70  
  Purchase #7 $232.87   6.577%   $248.1859   $248.19   $248.20   $248.20  
  7 purchase totals = $1,085.95       $1,162.1019   $1,162.11   $1,162.15   $1,162.20