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 $54.99   8.222%   $59.5113   $59.51   $59.50   $59.50  
  Purchase #2 $224.83   3.863%   $233.5152   $233.52   $233.50   $233.50  
  Purchase #3 $167.78   4.808%   $175.8469   $175.85   $175.85   $175.80  
  Purchase #4 $207.65   11.529%   $231.59   $231.59   $231.60   $231.60  
  Purchase #5 $218.51   8.323%   $236.6966   $236.70   $236.70   $236.70  
  Purchase #6 $38.49   4.282%   $40.1381   $40.14   $40.15   $40.10  
  Purchase #7 $211.81   11.280%   $235.7022   $235.70   $235.70   $235.70  
  7 purchase totals = $1,124.06       $1,213.0003   $1,213.01   $1,213.00   $1,212.90