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 $53.75   4.737%   $56.2961   $56.30   $56.30   $56.30  
  Purchase #2 $122.31   3.668%   $126.7963   $126.80   $126.80   $126.80  
  Purchase #3 $206.33   9.727%   $226.3997   $226.40   $226.40   $226.40  
  Purchase #4 $165.49   5.137%   $173.9912   $173.99   $174.00   $174.00  
  Purchase #5 $199.75   6.446%   $212.6259   $212.63   $212.65   $212.60  
  Purchase #6 $41.48   10.255%   $45.7338   $45.73   $45.75   $45.70  
  Purchase #7 $115.61   3.215%   $119.3269   $119.33   $119.35   $119.30  
  7 purchase totals = $904.72       $961.1699   $961.18   $961.25   $961.10