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 $183.68   5.152%   $193.1432   $193.14   $193.15   $193.10  
  Purchase #2 $167.50   13.534%   $190.1695   $190.17   $190.15   $190.20  
  Purchase #3 $11.58   8.703%   $12.5878   $12.59   $12.60   $12.60  
  Purchase #4 $197.78   4.402%   $206.4863   $206.49   $206.50   $206.50  
  Purchase #5 $156.35   6.699%   $166.8239   $166.82   $166.80   $166.80  
  Purchase #6 $136.62   5.192%   $143.7133   $143.71   $143.70   $143.70  
  Purchase #7 $133.67   5.128%   $140.5246   $140.52   $140.50   $140.50  
  7 purchase totals = $987.18       $1,053.4486   $1,053.44   $1,053.40   $1,053.40