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 $58.60   7.641%   $63.0776   $63.08   $63.10   $63.10  
  Purchase #2 $89.29   6.108%   $94.7438   $94.74   $94.75   $94.70  
  Purchase #3 $125.37   10.482%   $138.5113   $138.51   $138.50   $138.50  
  Purchase #4 $23.86   9.709%   $26.1766   $26.18   $26.20   $26.20  
  Purchase #5 $6.41   8.360%   $6.9459   $6.95   $6.95   $6.90  
  Purchase #6 $186.90   13.800%   $212.6922   $212.69   $212.70   $212.70  
  Purchase #7 $50.65   12.456%   $56.959   $56.96   $56.95   $57.00  
  7 purchase totals = $541.08       $599.1064   $599.11   $599.15   $599.10