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 $87.87   5.796%   $92.9629   $92.96   $92.95   $93.00  
  Purchase #2 $199.60   13.566%   $226.6777   $226.68   $226.70   $226.70  
  Purchase #3 $42.82   3.461%   $44.302   $44.30   $44.30   $44.30  
  Purchase #4 $109.62   10.272%   $120.8802   $120.88   $120.90   $120.90  
  Purchase #5 $172.27   4.713%   $180.3891   $180.39   $180.40   $180.40  
  Purchase #6 $208.45   6.683%   $222.3807   $222.38   $222.40   $222.40  
  Purchase #7 $60.82   4.183%   $63.3641   $63.36   $63.35   $63.40  
  7 purchase totals = $881.45       $950.9567   $950.95   $951.00   $951.10