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 $137.53   10.163%   $151.5072   $151.51   $151.50   $151.50  
  Purchase #2 $236.69   3.584%   $245.173   $245.17   $245.15   $245.20  
  Purchase #3 $216.90   13.615%   $246.4309   $246.43   $246.45   $246.40  
  Purchase #4 $174.76   3.110%   $180.195   $180.20   $180.20   $180.20  
  Purchase #5 $23.43   5.347%   $24.6828   $24.68   $24.70   $24.70  
  Purchase #6 $53.55   5.696%   $56.6002   $56.60   $56.60   $56.60  
  Purchase #7 $60.54   5.503%   $63.8715   $63.87   $63.85   $63.90  
  7 purchase totals = $903.40       $968.4606   $968.46   $968.45   $968.50