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 $142.69   13.293%   $161.6578   $161.66   $161.65   $161.70  
  Purchase #2 $143.59   6.454%   $152.8573   $152.86   $152.85   $152.90  
  Purchase #3 $85.70   10.212%   $94.4517   $94.45   $94.45   $94.50  
  Purchase #4 $211.49   10.811%   $234.3542   $234.35   $234.35   $234.40  
  Purchase #5 $24.50   5.306%   $25.8   $25.80   $25.80   $25.80  
  Purchase #6 $241.81   12.192%   $271.2915   $271.29   $271.30   $271.30  
  Purchase #7 $222.87   11.619%   $248.7653   $248.77   $248.75   $248.80  
  7 purchase totals = $1,072.65       $1,189.1778   $1,189.18   $1,189.15   $1,189.40