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 $61.40   8.225%   $66.4502   $66.45   $66.45   $66.50  
  Purchase #2 $236.41   6.383%   $251.5001   $251.50   $251.50   $251.50  
  Purchase #3 $196.81   3.446%   $203.5921   $203.59   $203.60   $203.60  
  Purchase #4 $235.87   3.155%   $243.3117   $243.31   $243.30   $243.30  
  Purchase #5 $134.99   8.815%   $146.8894   $146.89   $146.90   $146.90  
  Purchase #6 $35.87   3.169%   $37.0067   $37.01   $37.00   $37.00  
  Purchase #7 $247.26   12.328%   $277.7422   $277.74   $277.75   $277.70  
  7 purchase totals = $1,148.61       $1,226.4924   $1,226.49   $1,226.50   $1,226.50