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 $56.27   3.310%   $58.1325   $58.13   $58.15   $58.10  
  Purchase #2 $122.41   8.214%   $132.4648   $132.46   $132.45   $132.50  
  Purchase #3 $18.51   5.277%   $19.4868   $19.49   $19.50   $19.50  
  Purchase #4 $199.45   3.219%   $205.8703   $205.87   $205.85   $205.90  
  Purchase #5 $153.89   5.200%   $161.8923   $161.89   $161.90   $161.90  
  Purchase #6 $248.84   13.363%   $282.0925   $282.09   $282.10   $282.10  
  Purchase #7 $171.80   8.377%   $186.1917   $186.19   $186.20   $186.20  
  7 purchase totals = $971.17       $1,046.1309   $1,046.12   $1,046.15   $1,046.20