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 $58.86   3.283%   $60.7924   $60.79   $60.80   $60.80  
  Purchase #2 $212.32   10.459%   $234.5265   $234.53   $234.55   $234.50  
  Purchase #3 $41.99   13.676%   $47.7326   $47.73   $47.75   $47.70  
  Purchase #4 $241.82   9.398%   $264.5462   $264.55   $264.55   $264.50  
  Purchase #5 $188.29   10.227%   $207.5464   $207.55   $207.55   $207.50  
  Purchase #6 $9.39   3.408%   $9.71   $9.71   $9.70   $9.70  
  Purchase #7 $151.25   12.456%   $170.0897   $170.09   $170.10   $170.10  
  7 purchase totals = $903.92       $994.9438   $994.95   $995.00   $994.80