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 $186.81   3.188%   $192.7655   $192.77   $192.75   $192.80  
  Purchase #2 $54.31   4.143%   $56.5601   $56.56   $56.55   $56.60  
  Purchase #3 $177.38   13.599%   $201.5019   $201.50   $201.50   $201.50  
  Purchase #4 $242.37   5.610%   $255.967   $255.97   $255.95   $256.00  
  Purchase #5 $61.49   3.851%   $63.858   $63.86   $63.85   $63.90  
  Purchase #6 $120.74   6.104%   $128.11   $128.11   $128.10   $128.10  
  Purchase #7 $196.65   11.721%   $219.6993   $219.70   $219.70   $219.70  
  7 purchase totals = $1,039.75       $1,118.4618   $1,118.47   $1,118.40   $1,118.60