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 $202.57   11.567%   $226.0013   $226.00   $226.00   $226.00  
  Purchase #2 $85.37   10.716%   $94.5182   $94.52   $94.50   $94.50  
  Purchase #3 $100.48   3.516%   $104.0129   $104.01   $104.00   $104.00  
  Purchase #4 $73.47   12.615%   $82.7382   $82.74   $82.75   $82.70  
  Purchase #5 $198.65   6.323%   $211.2106   $211.21   $211.20   $211.20  
  Purchase #6 $77.38   3.132%   $79.8035   $79.80   $79.80   $79.80  
  Purchase #7 $119.55   5.646%   $126.2998   $126.30   $126.30   $126.30  
  7 purchase totals = $857.47       $924.5845   $924.58   $924.55   $924.50