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 $187.73   8.114%   $202.9624   $202.96   $202.95   $203.00  
  Purchase #2 $53.94   4.829%   $56.5448   $56.54   $56.55   $56.50  
  Purchase #3 $119.69   6.418%   $127.3717   $127.37   $127.35   $127.40  
  Purchase #4 $211.48   10.390%   $233.4528   $233.45   $233.45   $233.50  
  Purchase #5 $215.89   8.640%   $234.5429   $234.54   $234.55   $234.50  
  Purchase #6 $32.35   3.627%   $33.5233   $33.52   $33.50   $33.50  
  Purchase #7 $34.91   4.387%   $36.4415   $36.44   $36.45   $36.40  
  7 purchase totals = $855.99       $924.8394   $924.82   $924.80   $924.80