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 $48.66   7.174%   $52.1509   $52.15   $52.15   $52.20  
  Purchase #2 $8.41   6.344%   $8.9435   $8.94   $8.95   $8.90  
  Purchase #3 $41.48   8.743%   $45.1066   $45.11   $45.10   $45.10  
  Purchase #4 $196.41   5.161%   $206.5467   $206.55   $206.55   $206.50  
  Purchase #5 $44.88   9.782%   $49.2702   $49.27   $49.25   $49.30  
  Purchase #6 $198.35   11.394%   $220.95   $220.95   $220.95   $221.00  
  Purchase #7 $145.65   3.260%   $150.3982   $150.40   $150.40   $150.40  
  7 purchase totals = $683.84       $733.3661   $733.37   $733.35   $733.40