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 $228.67   9.602%   $250.6269   $250.63   $250.65   $250.60  
  Purchase #2 $143.92   12.467%   $161.8625   $161.86   $161.85   $161.90  
  Purchase #3 $232.94   9.169%   $254.2983   $254.30   $254.30   $254.30  
  Purchase #4 $185.96   11.727%   $207.7675   $207.77   $207.75   $207.80  
  Purchase #5 $209.36   7.806%   $225.7026   $225.70   $225.70   $225.70  
  Purchase #6 $190.86   6.335%   $202.951   $202.95   $202.95   $203.00  
  Purchase #7 $120.66   4.809%   $126.4625   $126.46   $126.45   $126.50  
  7 purchase totals = $1,312.37       $1,429.6713   $1,429.67   $1,429.65   $1,429.80