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 $49.93   6.770%   $53.3103   $53.31   $53.30   $53.30  
  Purchase #2 $211.82   10.848%   $234.7982   $234.80   $234.80   $234.80  
  Purchase #3 $138.69   8.478%   $150.4481   $150.45   $150.45   $150.40  
  Purchase #4 $190.89   7.331%   $204.8841   $204.88   $204.90   $204.90  
  Purchase #5 $164.41   7.741%   $177.137   $177.14   $177.15   $177.10  
  Purchase #6 $35.55   7.623%   $38.26   $38.26   $38.25   $38.30  
  Purchase #7 $166.86   12.681%   $188.0195   $188.02   $188.00   $188.00  
  7 purchase totals = $958.15       $1,046.8572   $1,046.86   $1,046.85   $1,046.80