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 $213.31   4.760%   $223.4636   $223.46   $223.45   $223.50  
  Purchase #2 $214.59   6.626%   $228.8087   $228.81   $228.80   $228.80  
  Purchase #3 $181.97   7.872%   $196.2947   $196.29   $196.30   $196.30  
  Purchase #4 $44.28   9.300%   $48.398   $48.40   $48.40   $48.40  
  Purchase #5 $52.71   7.300%   $56.5578   $56.56   $56.55   $56.60  
  Purchase #6 $125.32   8.151%   $135.5348   $135.53   $135.55   $135.50  
  Purchase #7 $207.97   9.827%   $228.4072   $228.41   $228.40   $228.40  
  7 purchase totals = $1,040.15       $1,117.4648   $1,117.46   $1,117.45   $1,117.50