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 $47.39   10.543%   $52.3863   $52.39   $52.40   $52.40  
  Purchase #2 $114.31   7.733%   $123.1496   $123.15   $123.15   $123.10  
  Purchase #3 $174.52   6.530%   $185.9162   $185.92   $185.90   $185.90  
  Purchase #4 $111.86   5.564%   $118.0839   $118.08   $118.10   $118.10  
  Purchase #5 $124.67   4.678%   $130.5021   $130.50   $130.50   $130.50  
  Purchase #6 $198.44   3.797%   $205.9748   $205.97   $205.95   $206.00  
  Purchase #7 $191.57   5.443%   $201.9972   $202.00   $202.00   $202.00  
  7 purchase totals = $962.76       $1,018.0101   $1,018.01   $1,018.00   $1,018.00