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 $95.67   8.278%   $103.5896   $103.59   $103.60   $103.60  
  Purchase #2 $84.82   7.117%   $90.8566   $90.86   $90.85   $90.90  
  Purchase #3 $68.95   11.767%   $77.0633   $77.06   $77.05   $77.10  
  Purchase #4 $22.71   13.793%   $25.8424   $25.84   $25.85   $25.80  
  Purchase #5 $126.81   5.825%   $134.1967   $134.20   $134.20   $134.20  
  Purchase #6 $96.63   8.873%   $105.204   $105.20   $105.20   $105.20  
  Purchase #7 $195.58   11.623%   $218.3123   $218.31   $218.30   $218.30  
  7 purchase totals = $691.17       $755.0649   $755.06   $755.05   $755.10