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 $121.44   4.758%   $127.2181   $127.22   $127.20   $127.20  
  Purchase #2 $165.67   5.580%   $174.9144   $174.91   $174.90   $174.90  
  Purchase #3 $32.80   4.705%   $34.3432   $34.34   $34.35   $34.30  
  Purchase #4 $151.70   9.848%   $166.6394   $166.64   $166.65   $166.60  
  Purchase #5 $54.81   6.115%   $58.1616   $58.16   $58.15   $58.20  
  Purchase #6 $39.67   4.231%   $41.3484   $41.35   $41.35   $41.30  
  Purchase #7 $201.35   6.294%   $214.023   $214.02   $214.00   $214.00  
  7 purchase totals = $767.44       $816.6481   $816.64   $816.60   $816.50