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 $220.56   9.274%   $241.0147   $241.01   $241.00   $241.00  
  Purchase #2 $192.27   12.648%   $216.5883   $216.59   $216.60   $216.60  
  Purchase #3 $15.28   4.320%   $15.9401   $15.94   $15.95   $15.90  
  Purchase #4 $169.81   5.582%   $179.2888   $179.29   $179.30   $179.30  
  Purchase #5 $186.81   8.623%   $202.9186   $202.92   $202.90   $202.90  
  Purchase #6 $246.98   3.499%   $255.6218   $255.62   $255.60   $255.60  
  Purchase #7 $106.94   6.617%   $114.0162   $114.02   $114.00   $114.00  
  7 purchase totals = $1,138.65       $1,225.3885   $1,225.39   $1,225.35   $1,225.30