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 $127.74   13.521%   $145.0117   $145.01   $145.00   $145.00  
  Purchase #2 $39.95   5.328%   $42.0785   $42.08   $42.10   $42.10  
  Purchase #3 $75.61   8.363%   $81.9333   $81.93   $81.95   $81.90  
  Purchase #4 $65.60   11.211%   $72.9544   $72.95   $72.95   $73.00  
  Purchase #5 $209.67   7.795%   $226.0138   $226.01   $226.00   $226.00  
  Purchase #6 $208.98   11.597%   $233.2154   $233.22   $233.20   $233.20  
  Purchase #7 $216.61   12.187%   $243.0083   $243.01   $243.00   $243.00  
  7 purchase totals = $944.16       $1,044.2154   $1,044.21   $1,044.20   $1,044.20