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 $65.98   11.133%   $73.3256   $73.33   $73.35   $73.30  
  Purchase #2 $40.92   8.215%   $44.2816   $44.28   $44.30   $44.30  
  Purchase #3 $72.41   11.605%   $80.8132   $80.81   $80.80   $80.80  
  Purchase #4 $84.60   9.522%   $92.6556   $92.66   $92.65   $92.70  
  Purchase #5 $240.61   10.453%   $265.761   $265.76   $265.75   $265.80  
  Purchase #6 $198.96   13.327%   $225.4754   $225.48   $225.50   $225.50  
  Purchase #7 $219.43   11.129%   $243.8504   $243.85   $243.85   $243.90  
  7 purchase totals = $922.91       $1,026.1628   $1,026.17   $1,026.20   $1,026.30