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 $61.25   6.457%   $65.2049   $65.20   $65.20   $65.20  
  Purchase #2 $70.84   13.581%   $80.4608   $80.46   $80.45   $80.50  
  Purchase #3 $123.48   6.841%   $131.9273   $131.93   $131.95   $131.90  
  Purchase #4 $100.63   6.470%   $107.1408   $107.14   $107.15   $107.10  
  Purchase #5 $141.36   13.552%   $160.5171   $160.52   $160.50   $160.50  
  Purchase #6 $248.66   11.672%   $277.6836   $277.68   $277.70   $277.70  
  Purchase #7 $179.40   12.218%   $201.3191   $201.32   $201.30   $201.30  
  7 purchase totals = $925.62       $1,024.2536   $1,024.25   $1,024.25   $1,024.20