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 $193.99   6.810%   $207.2007   $207.20   $207.20   $207.20  
  Purchase #2 $242.54   8.205%   $262.4404   $262.44   $262.45   $262.40  
  Purchase #3 $19.30   6.249%   $20.5061   $20.51   $20.50   $20.50  
  Purchase #4 $8.80   10.340%   $9.7099   $9.71   $9.70   $9.70  
  Purchase #5 $216.83   10.715%   $240.0633   $240.06   $240.05   $240.10  
  Purchase #6 $25.95   12.746%   $29.2576   $29.26   $29.25   $29.30  
  Purchase #7 $249.79   4.294%   $260.516   $260.52   $260.50   $260.50  
  7 purchase totals = $957.20       $1,029.6940   $1,029.70   $1,029.65   $1,029.70