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 $216.80   12.505%   $243.9108   $243.91   $243.90   $243.90  
  Purchase #2 $147.93   8.343%   $160.2718   $160.27   $160.25   $160.30  
  Purchase #3 $52.97   4.195%   $55.1921   $55.19   $55.20   $55.20  
  Purchase #4 $70.57   7.236%   $75.6764   $75.68   $75.70   $75.70  
  Purchase #5 $204.65   4.796%   $214.465   $214.47   $214.45   $214.50  
  Purchase #6 $235.73   11.605%   $263.0865   $263.09   $263.10   $263.10  
  Purchase #7 $35.93   13.651%   $40.8348   $40.83   $40.85   $40.80  
  7 purchase totals = $964.58       $1,053.4374   $1,053.44   $1,053.45   $1,053.50