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 $235.36   8.124%   $254.4806   $254.48   $254.50   $254.50  
  Purchase #2 $168.46   11.279%   $187.4606   $187.46   $187.45   $187.50  
  Purchase #3 $96.69   13.242%   $109.4937   $109.49   $109.50   $109.50  
  Purchase #4 $231.59   3.492%   $239.6771   $239.68   $239.70   $239.70  
  Purchase #5 $146.75   5.280%   $154.4984   $154.50   $154.50   $154.50  
  Purchase #6 $191.31   6.561%   $203.8618   $203.86   $203.85   $203.90  
  Purchase #7 $53.28   10.628%   $58.9426   $58.94   $58.95   $58.90  
  7 purchase totals = $1,123.44       $1,208.4148   $1,208.41   $1,208.45   $1,208.50