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 $57.37   10.525%   $63.4082   $63.41   $63.40   $63.40  
  Purchase #2 $212.69   12.523%   $239.3252   $239.33   $239.35   $239.30  
  Purchase #3 $204.46   12.458%   $229.9316   $229.93   $229.95   $229.90  
  Purchase #4 $232.80   3.814%   $241.679   $241.68   $241.70   $241.70  
  Purchase #5 $225.29   3.252%   $232.6164   $232.62   $232.60   $232.60  
  Purchase #6 $211.61   9.339%   $231.3723   $231.37   $231.35   $231.40  
  Purchase #7 $179.87   4.599%   $188.1422   $188.14   $188.15   $188.10  
  7 purchase totals = $1,324.09       $1,426.4749   $1,426.48   $1,426.50   $1,426.40