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 $56.61   12.304%   $63.5753   $63.58   $63.60   $63.60  
  Purchase #2 $213.42   11.716%   $238.4243   $238.42   $238.40   $238.40  
  Purchase #3 $33.55   4.577%   $35.0856   $35.09   $35.10   $35.10  
  Purchase #4 $201.62   12.112%   $226.0402   $226.04   $226.05   $226.00  
  Purchase #5 $248.65   9.445%   $272.135   $272.14   $272.15   $272.10  
  Purchase #6 $171.91   5.823%   $181.9203   $181.92   $181.90   $181.90  
  Purchase #7 $63.28   4.438%   $66.0884   $66.09   $66.10   $66.10  
  7 purchase totals = $989.04       $1,083.2691   $1,083.28   $1,083.30   $1,083.20