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 $231.60   4.346%   $241.6653   $241.67   $241.65   $241.70  
  Purchase #2 $10.70   11.190%   $11.8973   $11.90   $11.90   $11.90  
  Purchase #3 $57.53   8.626%   $62.4925   $62.49   $62.50   $62.50  
  Purchase #4 $220.35   6.754%   $235.2324   $235.23   $235.25   $235.20  
  Purchase #5 $185.88   9.217%   $203.0126   $203.01   $203.00   $203.00  
  Purchase #6 $217.34   4.851%   $227.8832   $227.88   $227.90   $227.90  
  Purchase #7 $55.46   10.111%   $61.0676   $61.07   $61.05   $61.10  
  7 purchase totals = $978.86       $1,043.2509   $1,043.25   $1,043.25   $1,043.30