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 $23.84   12.526%   $26.8262   $26.83   $26.85   $26.80  
  Purchase #2 $201.28   9.583%   $220.5687   $220.57   $220.55   $220.60  
  Purchase #3 $59.65   8.308%   $64.6057   $64.61   $64.60   $64.60  
  Purchase #4 $220.78   7.297%   $236.8903   $236.89   $236.90   $236.90  
  Purchase #5 $207.32   11.776%   $231.734   $231.73   $231.75   $231.70  
  Purchase #6 $36.25   11.297%   $40.3452   $40.35   $40.35   $40.30  
  Purchase #7 $177.80   11.409%   $198.0852   $198.09   $198.10   $198.10  
  7 purchase totals = $926.92       $1,019.0553   $1,019.07   $1,019.10   $1,019.00