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 $226.84   10.169%   $249.9074   $249.91   $249.90   $249.90  
  Purchase #2 $195.70   8.614%   $212.5576   $212.56   $212.55   $212.60  
  Purchase #3 $218.48   8.218%   $236.4347   $236.43   $236.45   $236.40  
  Purchase #4 $35.31   12.627%   $39.7686   $39.77   $39.75   $39.80  
  Purchase #5 $204.91   5.661%   $216.51   $216.51   $216.50   $216.50  
  Purchase #6 $79.50   9.634%   $87.159   $87.16   $87.15   $87.20  
  Purchase #7 $241.31   4.620%   $252.4585   $252.46   $252.45   $252.50  
  7 purchase totals = $1,202.05       $1,294.7958   $1,294.80   $1,294.75   $1,294.90