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 $196.83   4.259%   $205.213   $205.21   $205.20   $205.20  
  Purchase #2 $226.25   13.524%   $256.8481   $256.85   $256.85   $256.80  
  Purchase #3 $140.42   6.301%   $149.2679   $149.27   $149.25   $149.30  
  Purchase #4 $212.52   12.687%   $239.4824   $239.48   $239.50   $239.50  
  Purchase #5 $199.70   13.300%   $226.2601   $226.26   $226.25   $226.30  
  Purchase #6 $53.70   13.646%   $61.0279   $61.03   $61.05   $61.00  
  Purchase #7 $210.74   8.614%   $228.8931   $228.89   $228.90   $228.90  
  7 purchase totals = $1,240.16       $1,366.9925   $1,366.99   $1,367.00   $1,367.00