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 $227.98   13.620%   $259.0309   $259.03   $259.05   $259.00  
  Purchase #2 $168.25   5.167%   $176.9435   $176.94   $176.95   $176.90  
  Purchase #3 $101.52   7.279%   $108.9096   $108.91   $108.90   $108.90  
  Purchase #4 $127.94   8.208%   $138.4413   $138.44   $138.45   $138.40  
  Purchase #5 $45.79   5.406%   $48.2654   $48.27   $48.25   $48.30  
  Purchase #6 $134.52   9.654%   $147.5066   $147.51   $147.50   $147.50  
  Purchase #7 $237.77   11.855%   $265.9576   $265.96   $265.95   $266.00  
  7 purchase totals = $1,043.77       $1,145.0549   $1,145.06   $1,145.05   $1,145.00