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 $238.49   11.864%   $266.7845   $266.78   $266.80   $266.80  
  Purchase #2 $214.64   3.693%   $222.5667   $222.57   $222.55   $222.60  
  Purchase #3 $69.44   11.823%   $77.6499   $77.65   $77.65   $77.60  
  Purchase #4 $113.27   9.453%   $123.9774   $123.98   $124.00   $124.00  
  Purchase #5 $68.55   13.543%   $77.8337   $77.83   $77.85   $77.80  
  Purchase #6 $57.33   11.432%   $63.884   $63.88   $63.90   $63.90  
  Purchase #7 $193.69   11.808%   $216.5609   $216.56   $216.55   $216.60  
  7 purchase totals = $955.41       $1,049.2571   $1,049.25   $1,049.30   $1,049.30