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 $134.40   10.615%   $148.6666   $148.67   $148.65   $148.70  
  Purchase #2 $179.44   4.182%   $186.9442   $186.94   $186.95   $186.90  
  Purchase #3 $72.63   4.580%   $75.9565   $75.96   $75.95   $76.00  
  Purchase #4 $176.52   12.772%   $199.0651   $199.07   $199.05   $199.10  
  Purchase #5 $214.56   10.750%   $237.6252   $237.63   $237.65   $237.60  
  Purchase #6 $153.57   11.779%   $171.659   $171.66   $171.65   $171.70  
  Purchase #7 $220.32   12.560%   $247.9922   $247.99   $248.00   $248.00  
  7 purchase totals = $1,151.44       $1,267.9088   $1,267.92   $1,267.90   $1,268.00