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 $97.81   10.796%   $108.3696   $108.37   $108.35   $108.40  
  Purchase #2 $55.27   9.861%   $60.7202   $60.72   $60.70   $60.70  
  Purchase #3 $33.25   4.696%   $34.8114   $34.81   $34.80   $34.80  
  Purchase #4 $109.78   9.799%   $120.5373   $120.54   $120.55   $120.50  
  Purchase #5 $148.43   11.270%   $165.1581   $165.16   $165.15   $165.20  
  Purchase #6 $231.30   4.316%   $241.2829   $241.28   $241.30   $241.30  
  Purchase #7 $28.65   12.181%   $32.1399   $32.14   $32.15   $32.10  
  7 purchase totals = $704.49       $763.0194   $763.02   $763.00   $763.00