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 $59.38   9.229%   $64.8602   $64.86   $64.85   $64.90  
  Purchase #2 $246.33   7.150%   $263.9426   $263.94   $263.95   $263.90  
  Purchase #3 $125.88   13.651%   $143.0639   $143.06   $143.05   $143.10  
  Purchase #4 $120.69   10.658%   $133.5531   $133.55   $133.55   $133.60  
  Purchase #5 $70.57   9.467%   $77.2509   $77.25   $77.25   $77.30  
  Purchase #6 $184.67   7.344%   $198.2322   $198.23   $198.25   $198.20  
  Purchase #7 $73.48   7.574%   $79.0454   $79.05   $79.05   $79.00  
  7 purchase totals = $881.00       $959.9483   $959.94   $959.95   $960.00