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 $47.25   7.751%   $50.9123   $50.91   $50.90   $50.90  
  Purchase #2 $240.47   9.225%   $262.6534   $262.65   $262.65   $262.70  
  Purchase #3 $166.94   4.410%   $174.3021   $174.30   $174.30   $174.30  
  Purchase #4 $49.89   4.831%   $52.3002   $52.30   $52.30   $52.30  
  Purchase #5 $232.83   3.115%   $240.0827   $240.08   $240.10   $240.10  
  Purchase #6 $79.55   4.186%   $82.88   $82.88   $82.90   $82.90  
  Purchase #7 $66.70   4.583%   $69.7569   $69.76   $69.75   $69.80  
  7 purchase totals = $883.63       $932.8876   $932.88   $932.90   $933.00