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 $59.47   6.414%   $63.2844   $63.28   $63.30   $63.30  
  Purchase #2 $232.26   7.809%   $250.3972   $250.40   $250.40   $250.40  
  Purchase #3 $41.61   10.210%   $45.8584   $45.86   $45.85   $45.90  
  Purchase #4 $67.83   8.475%   $73.5786   $73.58   $73.60   $73.60  
  Purchase #5 $221.88   6.835%   $237.0455   $237.05   $237.05   $237.00  
  Purchase #6 $210.68   9.231%   $230.1279   $230.13   $230.15   $230.10  
  Purchase #7 $248.32   6.179%   $263.6637   $263.66   $263.65   $263.70  
  7 purchase totals = $1,082.05       $1,163.9557   $1,163.96   $1,164.00   $1,164.00