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 $5.80   4.788%   $6.0777   $6.08   $6.10   $6.10  
  Purchase #2 $127.65   5.329%   $134.4525   $134.45   $134.45   $134.50  
  Purchase #3 $66.50   9.827%   $73.035   $73.04   $73.05   $73.00  
  Purchase #4 $60.50   7.389%   $64.9703   $64.97   $64.95   $65.00  
  Purchase #5 $130.73   6.261%   $138.915   $138.92   $138.90   $138.90  
  Purchase #6 $191.92   12.311%   $215.5473   $215.55   $215.55   $215.50  
  Purchase #7 $66.73   5.654%   $70.5029   $70.50   $70.50   $70.50  
  7 purchase totals = $649.83       $703.5007   $703.51   $703.50   $703.50