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 $237.94   11.530%   $265.3745   $265.37   $265.35   $265.40  
  Purchase #2 $64.69   7.502%   $69.543   $69.54   $69.55   $69.50  
  Purchase #3 $207.88   5.158%   $218.6025   $218.60   $218.60   $218.60  
  Purchase #4 $113.74   5.384%   $119.8638   $119.86   $119.85   $119.90  
  Purchase #5 $144.76   11.229%   $161.0151   $161.02   $161.00   $161.00  
  Purchase #6 $126.50   12.297%   $142.0557   $142.06   $142.05   $142.10  
  Purchase #7 $34.52   11.158%   $38.3717   $38.37   $38.35   $38.40  
  7 purchase totals = $930.03       $1,014.8263   $1,014.82   $1,014.75   $1,014.90