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 $60.58   3.867%   $62.9226   $62.92   $62.90   $62.90  
  Purchase #2 $86.65   12.613%   $97.5792   $97.58   $97.60   $97.60  
  Purchase #3 $246.50   9.312%   $269.4541   $269.45   $269.45   $269.50  
  Purchase #4 $100.44   9.191%   $109.6714   $109.67   $109.65   $109.70  
  Purchase #5 $44.58   3.481%   $46.1318   $46.13   $46.15   $46.10  
  Purchase #6 $13.73   3.603%   $14.2247   $14.22   $14.20   $14.20  
  Purchase #7 $181.76   9.112%   $198.322   $198.32   $198.30   $198.30  
  7 purchase totals = $734.24       $798.3058   $798.29   $798.25   $798.30