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 $73.71   4.574%   $77.0815   $77.08   $77.10   $77.10  
  Purchase #2 $190.89   8.767%   $207.6253   $207.63   $207.65   $207.60  
  Purchase #3 $221.36   4.591%   $231.5226   $231.52   $231.50   $231.50  
  Purchase #4 $228.25   3.261%   $235.6932   $235.69   $235.70   $235.70  
  Purchase #5 $201.57   8.181%   $218.0604   $218.06   $218.05   $218.10  
  Purchase #6 $247.28   9.749%   $271.3873   $271.39   $271.40   $271.40  
  Purchase #7 $9.34   11.433%   $10.4078   $10.41   $10.40   $10.40  
  7 purchase totals = $1,172.40       $1,251.7781   $1,251.78   $1,251.80   $1,251.80