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 $160.40   10.183%   $176.7335   $176.73   $176.75   $176.70  
  Purchase #2 $169.80   13.446%   $192.6313   $192.63   $192.65   $192.60  
  Purchase #3 $220.34   3.273%   $227.5517   $227.55   $227.55   $227.60  
  Purchase #4 $71.84   11.250%   $79.922   $79.92   $79.90   $79.90  
  Purchase #5 $106.43   3.619%   $110.2817   $110.28   $110.30   $110.30  
  Purchase #6 $231.74   5.268%   $243.9481   $243.95   $243.95   $243.90  
  Purchase #7 $144.69   13.588%   $164.3505   $164.35   $164.35   $164.40  
  7 purchase totals = $1,105.24       $1,195.4188   $1,195.41   $1,195.45   $1,195.40