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 $53.44   11.557%   $59.6161   $59.62   $59.60   $59.60  
  Purchase #2 $77.54   6.803%   $82.815   $82.82   $82.80   $82.80  
  Purchase #3 $220.86   12.268%   $247.9551   $247.96   $247.95   $248.00  
  Purchase #4 $120.59   12.509%   $135.6746   $135.67   $135.65   $135.70  
  Purchase #5 $201.40   9.104%   $219.7355   $219.74   $219.75   $219.70  
  Purchase #6 $50.62   5.570%   $53.4395   $53.44   $53.45   $53.40  
  Purchase #7 $41.75   8.491%   $45.295   $45.30   $45.30   $45.30  
  7 purchase totals = $766.20       $844.5308   $844.55   $844.50   $844.50