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 $218.66   10.264%   $241.1033   $241.10   $241.10   $241.10  
  Purchase #2 $112.55   6.300%   $119.6407   $119.64   $119.65   $119.60  
  Purchase #3 $215.71   5.229%   $226.9895   $226.99   $227.00   $227.00  
  Purchase #4 $25.29   12.631%   $28.4844   $28.48   $28.50   $28.50  
  Purchase #5 $204.46   4.432%   $213.5217   $213.52   $213.50   $213.50  
  Purchase #6 $152.58   13.477%   $173.1432   $173.14   $173.15   $173.10  
  Purchase #7 $17.35   12.683%   $19.5505   $19.55   $19.55   $19.60  
  7 purchase totals = $946.60       $1,022.4333   $1,022.42   $1,022.45   $1,022.40