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 $213.85   9.582%   $234.3411   $234.34   $234.35   $234.30  
  Purchase #2 $16.77   12.520%   $18.8696   $18.87   $18.85   $18.90  
  Purchase #3 $44.77   9.500%   $49.0232   $49.02   $49.00   $49.00  
  Purchase #4 $53.69   13.758%   $61.0767   $61.08   $61.10   $61.10  
  Purchase #5 $174.77   6.837%   $186.719   $186.72   $186.70   $186.70  
  Purchase #6 $72.89   9.205%   $79.5995   $79.60   $79.60   $79.60  
  Purchase #7 $125.64   12.512%   $141.3601   $141.36   $141.35   $141.40  
  7 purchase totals = $702.38       $770.9892   $770.99   $770.95   $771.00