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 $151.62   9.524%   $166.0603   $166.06   $166.05   $166.10  
  Purchase #2 $76.26   7.361%   $81.8735   $81.87   $81.85   $81.90  
  Purchase #3 $249.53   6.755%   $266.3858   $266.39   $266.40   $266.40  
  Purchase #4 $119.38   11.666%   $133.3069   $133.31   $133.30   $133.30  
  Purchase #5 $172.68   6.409%   $183.7471   $183.75   $183.75   $183.70  
  Purchase #6 $99.52   6.796%   $106.2834   $106.28   $106.30   $106.30  
  Purchase #7 $113.26   10.315%   $124.9428   $124.94   $124.95   $124.90  
  7 purchase totals = $982.25       $1,062.5998   $1,062.60   $1,062.60   $1,062.60