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 $55.57   8.462%   $60.2723   $60.27   $60.25   $60.30  
  Purchase #2 $95.67   6.168%   $101.5709   $101.57   $101.55   $101.60  
  Purchase #3 $227.91   6.635%   $243.0318   $243.03   $243.05   $243.00  
  Purchase #4 $150.96   3.347%   $156.0126   $156.01   $156.00   $156.00  
  Purchase #5 $224.75   6.699%   $239.806   $239.81   $239.80   $239.80  
  Purchase #6 $7.84   8.702%   $8.5222   $8.52   $8.50   $8.50  
  Purchase #7 $223.72   13.511%   $253.9468   $253.95   $253.95   $253.90  
  7 purchase totals = $986.42       $1,063.1626   $1,063.16   $1,063.10   $1,063.10