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 $84.59   10.476%   $93.4516   $93.45   $93.45   $93.50  
  Purchase #2 $70.33   6.172%   $74.6708   $74.67   $74.65   $74.70  
  Purchase #3 $164.61   13.508%   $186.8455   $186.85   $186.85   $186.80  
  Purchase #4 $212.40   11.736%   $237.3273   $237.33   $237.35   $237.30  
  Purchase #5 $105.69   7.248%   $113.3504   $113.35   $113.35   $113.40  
  Purchase #6 $120.87   3.396%   $124.9747   $124.97   $124.95   $125.00  
  Purchase #7 $75.61   13.842%   $86.0759   $86.08   $86.10   $86.10  
  7 purchase totals = $834.10       $916.6962   $916.70   $916.70   $916.80