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 $34.88   9.657%   $38.2484   $38.25   $38.25   $38.20  
  Purchase #2 $116.51   8.358%   $126.2479   $126.25   $126.25   $126.20  
  Purchase #3 $196.75   12.277%   $220.905   $220.91   $220.90   $220.90  
  Purchase #4 $106.84   8.240%   $115.6436   $115.64   $115.65   $115.60  
  Purchase #5 $48.84   8.564%   $53.0227   $53.02   $53.00   $53.00  
  Purchase #6 $129.45   13.841%   $147.3672   $147.37   $147.35   $147.40  
  Purchase #7 $230.29   5.651%   $243.3037   $243.30   $243.30   $243.30  
  7 purchase totals = $863.56       $944.7385   $944.74   $944.70   $944.60