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 $185.92   10.842%   $206.0774   $206.08   $206.10   $206.10  
  Purchase #2 $140.45   9.616%   $153.9557   $153.96   $153.95   $154.00  
  Purchase #3 $62.32   6.557%   $66.4063   $66.41   $66.40   $66.40  
  Purchase #4 $167.46   4.727%   $175.3758   $175.38   $175.40   $175.40  
  Purchase #5 $6.84   7.172%   $7.3306   $7.33   $7.35   $7.30  
  Purchase #6 $246.53   9.801%   $270.6924   $270.69   $270.70   $270.70  
  Purchase #7 $140.76   4.448%   $147.021   $147.02   $147.00   $147.00  
  7 purchase totals = $950.28       $1,026.8592   $1,026.87   $1,026.90   $1,026.90