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 $174.79   13.373%   $198.1647   $198.16   $198.15   $198.20  
  Purchase #2 $92.71   7.469%   $99.6345   $99.63   $99.65   $99.60  
  Purchase #3 $234.33   7.424%   $251.7267   $251.73   $251.75   $251.70  
  Purchase #4 $55.67   5.549%   $58.7591   $58.76   $58.75   $58.80  
  Purchase #5 $248.34   7.700%   $267.4622   $267.46   $267.45   $267.50  
  Purchase #6 $147.72   13.424%   $167.5499   $167.55   $167.55   $167.50  
  Purchase #7 $30.72   8.485%   $33.3266   $33.33   $33.35   $33.30  
  7 purchase totals = $984.28       $1,076.6237   $1,076.62   $1,076.65   $1,076.60