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 $48.53   9.705%   $53.2398   $53.24   $53.25   $53.20  
  Purchase #2 $250.83   7.404%   $269.4015   $269.40   $269.40   $269.40  
  Purchase #3 $209.65   3.579%   $217.1534   $217.15   $217.15   $217.20  
  Purchase #4 $9.95   4.166%   $10.3645   $10.36   $10.35   $10.40  
  Purchase #5 $220.28   3.529%   $228.0537   $228.05   $228.05   $228.10  
  Purchase #6 $155.93   5.463%   $164.4485   $164.45   $164.45   $164.40  
  Purchase #7 $103.96   12.807%   $117.2742   $117.27   $117.25   $117.30  
  7 purchase totals = $999.13       $1,059.9356   $1,059.92   $1,059.90   $1,060.00