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 $178.32   9.649%   $195.5261   $195.53   $195.55   $195.50  
  Purchase #2 $158.80   13.787%   $180.6938   $180.69   $180.70   $180.70  
  Purchase #3 $243.97   12.710%   $274.9786   $274.98   $275.00   $275.00  
  Purchase #4 $12.66   8.819%   $13.7765   $13.78   $13.80   $13.80  
  Purchase #5 $170.77   12.721%   $192.4937   $192.49   $192.50   $192.50  
  Purchase #6 $24.43   5.164%   $25.6916   $25.69   $25.70   $25.70  
  Purchase #7 $172.68   11.830%   $193.108   $193.11   $193.10   $193.10  
  7 purchase totals = $961.63       $1,076.2683   $1,076.27   $1,076.35   $1,076.30