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 $88.35   5.484%   $93.1951   $93.20   $93.20   $93.20  
  Purchase #2 $241.56   5.767%   $255.4908   $255.49   $255.50   $255.50  
  Purchase #3 $45.25   5.443%   $47.713   $47.71   $47.70   $47.70  
  Purchase #4 $244.82   11.581%   $273.1726   $273.17   $273.15   $273.20  
  Purchase #5 $175.33   6.269%   $186.3214   $186.32   $186.30   $186.30  
  Purchase #6 $20.64   3.785%   $21.4212   $21.42   $21.40   $21.40  
  Purchase #7 $44.27   5.274%   $46.6048   $46.60   $46.60   $46.60  
  7 purchase totals = $860.22       $923.9189   $923.91   $923.85   $923.90