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 $91.65   4.241%   $95.5369   $95.54   $95.55   $95.50  
  Purchase #2 $145.58   3.826%   $151.1499   $151.15   $151.15   $151.10  
  Purchase #3 $145.98   11.598%   $162.9108   $162.91   $162.90   $162.90  
  Purchase #4 $132.53   10.348%   $146.2442   $146.24   $146.25   $146.20  
  Purchase #5 $87.70   8.588%   $95.2317   $95.23   $95.25   $95.20  
  Purchase #6 $219.33   3.107%   $226.1446   $226.14   $226.15   $226.10  
  Purchase #7 $169.77   6.536%   $180.8662   $180.87   $180.85   $180.90  
  7 purchase totals = $992.54       $1,058.0843   $1,058.08   $1,058.10   $1,057.90