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 $55.93   4.149%   $58.2505   $58.25   $58.25   $58.30  
  Purchase #2 $239.69   12.270%   $269.1   $269.10   $269.10   $269.10  
  Purchase #3 $228.48   12.192%   $256.3363   $256.34   $256.35   $256.30  
  Purchase #4 $98.53   11.235%   $109.5998   $109.60   $109.60   $109.60  
  Purchase #5 $229.98   10.508%   $254.1463   $254.15   $254.15   $254.10  
  Purchase #6 $78.43   7.269%   $84.1311   $84.13   $84.15   $84.10  
  Purchase #7 $106.96   13.169%   $121.0456   $121.05   $121.05   $121.00  
  7 purchase totals = $1,038.00       $1,152.6096   $1,152.62   $1,152.65   $1,152.50