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 $54.47   12.193%   $61.1115   $61.11   $61.10   $61.10  
  Purchase #2 $94.55   7.383%   $101.5306   $101.53   $101.55   $101.50  
  Purchase #3 $116.31   11.840%   $130.0811   $130.08   $130.10   $130.10  
  Purchase #4 $224.95   8.396%   $243.8368   $243.84   $243.85   $243.80  
  Purchase #5 $129.42   12.426%   $145.5017   $145.50   $145.50   $145.50  
  Purchase #6 $168.57   5.428%   $177.72   $177.72   $177.70   $177.70  
  Purchase #7 $198.34   4.591%   $207.4458   $207.45   $207.45   $207.40  
  7 purchase totals = $986.61       $1,067.2275   $1,067.23   $1,067.25   $1,067.10