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 $50.77   8.778%   $55.2266   $55.23   $55.25   $55.20  
  Purchase #2 $243.48   6.570%   $259.4766   $259.48   $259.50   $259.50  
  Purchase #3 $81.33   4.648%   $85.1102   $85.11   $85.10   $85.10  
  Purchase #4 $101.65   6.144%   $107.8954   $107.90   $107.90   $107.90  
  Purchase #5 $208.59   9.517%   $228.4415   $228.44   $228.45   $228.40  
  Purchase #6 $246.30   5.534%   $259.9302   $259.93   $259.95   $259.90  
  Purchase #7 $66.67   10.499%   $73.6697   $73.67   $73.65   $73.70  
  7 purchase totals = $998.79       $1,069.7502   $1,069.76   $1,069.80   $1,069.70