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 $50.41   12.572%   $56.7475   $56.75   $56.75   $56.70  
  Purchase #2 $236.57   8.489%   $256.6524   $256.65   $256.65   $256.70  
  Purchase #3 $172.52   10.512%   $190.6553   $190.66   $190.65   $190.70  
  Purchase #4 $29.90   13.542%   $33.9491   $33.95   $33.95   $33.90  
  Purchase #5 $136.68   11.859%   $152.8889   $152.89   $152.90   $152.90  
  Purchase #6 $165.36   5.687%   $174.764   $174.76   $174.75   $174.80  
  Purchase #7 $77.97   9.138%   $85.0949   $85.09   $85.10   $85.10  
  7 purchase totals = $869.41       $950.7521   $950.75   $950.75   $950.80