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 $136.41   8.273%   $147.6952   $147.70   $147.70   $147.70  
  Purchase #2 $153.38   8.802%   $166.8805   $166.88   $166.90   $166.90  
  Purchase #3 $103.53   11.152%   $115.0757   $115.08   $115.10   $115.10  
  Purchase #4 $61.53   3.596%   $63.7426   $63.74   $63.75   $63.70  
  Purchase #5 $187.32   8.278%   $202.8263   $202.83   $202.85   $202.80  
  Purchase #6 $237.81   12.623%   $267.8288   $267.83   $267.85   $267.80  
  Purchase #7 $88.76   10.570%   $98.1419   $98.14   $98.15   $98.10  
  7 purchase totals = $968.74       $1,062.1910   $1,062.20   $1,062.30   $1,062.10