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 $234.39   12.247%   $263.0957   $263.10   $263.10   $263.10  
  Purchase #2 $165.93   13.278%   $187.9622   $187.96   $187.95   $188.00  
  Purchase #3 $46.68   7.755%   $50.3   $50.30   $50.30   $50.30  
  Purchase #4 $124.80   11.550%   $139.2144   $139.21   $139.20   $139.20  
  Purchase #5 $21.28   8.723%   $23.1363   $23.14   $23.15   $23.10  
  Purchase #6 $181.34   6.781%   $193.6367   $193.64   $193.65   $193.60  
  Purchase #7 $202.78   11.592%   $226.2863   $226.29   $226.30   $226.30  
  7 purchase totals = $977.20       $1,083.6316   $1,083.64   $1,083.65   $1,083.60