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 $64.99   13.410%   $73.7052   $73.71   $73.70   $73.70  
  Purchase #2 $182.95   13.123%   $206.9585   $206.96   $206.95   $207.00  
  Purchase #3 $46.64   3.333%   $48.1945   $48.19   $48.20   $48.20  
  Purchase #4 $176.40   8.765%   $191.8615   $191.86   $191.85   $191.90  
  Purchase #5 $24.50   10.542%   $27.0828   $27.08   $27.10   $27.10  
  Purchase #6 $187.62   7.161%   $201.0555   $201.06   $201.05   $201.10  
  Purchase #7 $10.51   12.231%   $11.7955   $11.80   $11.80   $11.80  
  7 purchase totals = $693.61       $760.6535   $760.66   $760.65   $760.80