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 $117.52   4.798%   $123.1586   $123.16   $123.15   $123.20  
  Purchase #2 $130.87   10.642%   $144.7972   $144.80   $144.80   $144.80  
  Purchase #3 $232.61   10.661%   $257.4086   $257.41   $257.40   $257.40  
  Purchase #4 $107.83   12.244%   $121.0327   $121.03   $121.05   $121.00  
  Purchase #5 $167.97   4.828%   $176.0796   $176.08   $176.10   $176.10  
  Purchase #6 $109.84   9.136%   $119.875   $119.88   $119.90   $119.90  
  Purchase #7 $108.95   11.287%   $121.2472   $121.25   $121.25   $121.20  
  7 purchase totals = $975.59       $1,063.5989   $1,063.61   $1,063.65   $1,063.60