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 $244.86   8.780%   $266.3587   $266.36   $266.35   $266.40  
  Purchase #2 $52.52   10.127%   $57.8387   $57.84   $57.85   $57.80  
  Purchase #3 $52.48   9.270%   $57.3449   $57.34   $57.35   $57.30  
  Purchase #4 $205.98   11.416%   $229.4947   $229.49   $229.50   $229.50  
  Purchase #5 $28.26   9.420%   $30.9221   $30.92   $30.90   $30.90  
  Purchase #6 $203.25   6.833%   $217.1381   $217.14   $217.15   $217.10  
  Purchase #7 $152.39   7.658%   $164.06   $164.06   $164.05   $164.10  
  7 purchase totals = $939.74       $1,023.1572   $1,023.15   $1,023.15   $1,023.10