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 $85.57   7.570%   $92.0476   $92.05   $92.05   $92.00  
  Purchase #2 $15.42   9.640%   $16.9065   $16.91   $16.90   $16.90  
  Purchase #3 $228.81   8.614%   $248.5197   $248.52   $248.50   $248.50  
  Purchase #4 $136.96   11.289%   $152.4214   $152.42   $152.40   $152.40  
  Purchase #5 $136.47   12.792%   $153.9272   $153.93   $153.95   $153.90  
  Purchase #6 $22.87   7.757%   $24.644   $24.64   $24.65   $24.60  
  Purchase #7 $154.31   4.705%   $161.5703   $161.57   $161.55   $161.60  
  7 purchase totals = $780.41       $850.0367   $850.04   $850.00   $849.90