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 $186.44   11.253%   $207.4201   $207.42   $207.40   $207.40  
  Purchase #2 $174.77   10.748%   $193.5543   $193.55   $193.55   $193.60  
  Purchase #3 $244.52   10.405%   $269.9623   $269.96   $269.95   $270.00  
  Purchase #4 $127.51   9.598%   $139.7484   $139.75   $139.75   $139.70  
  Purchase #5 $26.42   9.435%   $28.9127   $28.91   $28.90   $28.90  
  Purchase #6 $159.67   13.381%   $181.0354   $181.04   $181.05   $181.00  
  Purchase #7 $22.71   6.866%   $24.2693   $24.27   $24.25   $24.30  
  7 purchase totals = $942.04       $1,044.9025   $1,044.90   $1,044.85   $1,044.90