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 $23.51   12.673%   $26.4894   $26.49   $26.50   $26.50  
  Purchase #2 $52.48   8.816%   $57.1066   $57.11   $57.10   $57.10  
  Purchase #3 $246.45   13.451%   $279.6   $279.60   $279.60   $279.60  
  Purchase #4 $249.68   11.830%   $279.2171   $279.22   $279.20   $279.20  
  Purchase #5 $119.42   12.386%   $134.2114   $134.21   $134.20   $134.20  
  Purchase #6 $187.99   8.201%   $203.4071   $203.41   $203.40   $203.40  
  Purchase #7 $73.35   9.563%   $80.3645   $80.36   $80.35   $80.40  
  7 purchase totals = $952.88       $1,060.3961   $1,060.40   $1,060.35   $1,060.40