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 $58.58   3.284%   $60.5038   $60.50   $60.50   $60.50  
  Purchase #2 $60.91   6.324%   $64.7619   $64.76   $64.75   $64.80  
  Purchase #3 $241.74   3.702%   $250.6892   $250.69   $250.70   $250.70  
  Purchase #4 $40.43   7.167%   $43.3276   $43.33   $43.35   $43.30  
  Purchase #5 $234.96   4.277%   $245.0092   $245.01   $245.00   $245.00  
  Purchase #6 $24.90   3.795%   $25.845   $25.85   $25.85   $25.80  
  Purchase #7 $60.45   7.795%   $65.1621   $65.16   $65.15   $65.20  
  7 purchase totals = $721.97       $755.2988   $755.30   $755.30   $755.30