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 $56.27   11.847%   $62.9363   $62.94   $62.95   $62.90  
  Purchase #2 $106.62   11.603%   $118.9911   $118.99   $119.00   $119.00  
  Purchase #3 $191.90   11.813%   $214.5691   $214.57   $214.55   $214.60  
  Purchase #4 $132.81   7.714%   $143.055   $143.06   $143.05   $143.10  
  Purchase #5 $112.79   11.480%   $125.7383   $125.74   $125.75   $125.70  
  Purchase #6 $125.79   7.413%   $135.1148   $135.11   $135.10   $135.10  
  Purchase #7 $247.51   7.839%   $266.9123   $266.91   $266.90   $266.90  
  7 purchase totals = $973.69       $1,067.3169   $1,067.32   $1,067.30   $1,067.30