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 $149.46   11.652%   $166.8751   $166.88   $166.90   $166.90  
  Purchase #2 $118.82   6.330%   $126.3413   $126.34   $126.35   $126.30  
  Purchase #3 $168.33   3.632%   $174.4437   $174.44   $174.45   $174.40  
  Purchase #4 $57.54   10.368%   $63.5057   $63.51   $63.50   $63.50  
  Purchase #5 $148.34   9.276%   $162.1   $162.10   $162.10   $162.10  
  Purchase #6 $167.78   5.716%   $177.3703   $177.37   $177.35   $177.40  
  Purchase #7 $159.76   8.695%   $173.6511   $173.65   $173.65   $173.70  
  7 purchase totals = $970.03       $1,044.2872   $1,044.29   $1,044.30   $1,044.30