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 $68.39   11.581%   $76.3102   $76.31   $76.30   $76.30  
  Purchase #2 $185.98   9.787%   $204.1819   $204.18   $204.20   $204.20  
  Purchase #3 $191.76   3.305%   $198.0977   $198.10   $198.10   $198.10  
  Purchase #4 $156.45   10.195%   $172.4001   $172.40   $172.40   $172.40  
  Purchase #5 $95.35   11.160%   $105.9911   $105.99   $106.00   $106.00  
  Purchase #6 $55.72   8.578%   $60.4997   $60.50   $60.50   $60.50  
  Purchase #7 $116.91   8.152%   $126.4405   $126.44   $126.45   $126.40  
  7 purchase totals = $870.56       $943.9212   $943.92   $943.95   $943.90