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 $58.44   3.149%   $60.2803   $60.28   $60.30   $60.30  
  Purchase #2 $92.84   3.132%   $95.7477   $95.75   $95.75   $95.70  
  Purchase #3 $94.27   8.185%   $101.986   $101.99   $102.00   $102.00  
  Purchase #4 $16.90   12.604%   $19.0301   $19.03   $19.05   $19.00  
  Purchase #5 $227.97   3.121%   $235.0849   $235.08   $235.10   $235.10  
  Purchase #6 $174.43   6.520%   $185.8028   $185.80   $185.80   $185.80  
  Purchase #7 $213.37   8.230%   $230.9304   $230.93   $230.95   $230.90  
  7 purchase totals = $878.22       $928.8622   $928.86   $928.95   $928.80