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 $141.51   8.510%   $153.5525   $153.55   $153.55   $153.60  
  Purchase #2 $174.84   12.259%   $196.2736   $196.27   $196.25   $196.30  
  Purchase #3 $23.49   10.510%   $25.9588   $25.96   $25.95   $26.00  
  Purchase #4 $18.74   10.822%   $20.768   $20.77   $20.75   $20.80  
  Purchase #5 $227.56   3.211%   $234.867   $234.87   $234.85   $234.90  
  Purchase #6 $138.78   13.457%   $157.4556   $157.46   $157.45   $157.50  
  Purchase #7 $235.70   3.216%   $243.2801   $243.28   $243.30   $243.30  
  7 purchase totals = $960.62       $1,032.1556   $1,032.16   $1,032.10   $1,032.40