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 $198.57   6.449%   $211.3758   $211.38   $211.40   $211.40  
  Purchase #2 $8.66   10.293%   $9.5514   $9.55   $9.55   $9.60  
  Purchase #3 $188.28   7.391%   $202.1958   $202.20   $202.20   $202.20  
  Purchase #4 $57.34   11.692%   $64.0442   $64.04   $64.05   $64.00  
  Purchase #5 $120.54   6.709%   $128.627   $128.63   $128.65   $128.60  
  Purchase #6 $164.40   4.787%   $172.2698   $172.27   $172.25   $172.30  
  Purchase #7 $55.45   7.676%   $59.7063   $59.71   $59.70   $59.70  
  7 purchase totals = $793.24       $847.7703   $847.78   $847.80   $847.80