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 $153.41   13.536%   $174.1756   $174.18   $174.20   $174.20  
  Purchase #2 $163.38   10.138%   $179.9435   $179.94   $179.95   $179.90  
  Purchase #3 $112.91   4.507%   $117.9989   $118.00   $118.00   $118.00  
  Purchase #4 $167.97   11.277%   $186.912   $186.91   $186.90   $186.90  
  Purchase #5 $62.31   4.741%   $65.2641   $65.26   $65.25   $65.30  
  Purchase #6 $187.44   13.511%   $212.765   $212.77   $212.75   $212.80  
  Purchase #7 $120.50   8.608%   $130.8726   $130.87   $130.85   $130.90  
  7 purchase totals = $967.92       $1,067.9317   $1,067.93   $1,067.90   $1,068.00