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 $180.66   13.444%   $204.9479   $204.95   $204.95   $204.90  
  Purchase #2 $40.27   13.137%   $45.5603   $45.56   $45.55   $45.60  
  Purchase #3 $244.57   5.236%   $257.3757   $257.38   $257.40   $257.40  
  Purchase #4 $59.93   7.794%   $64.6009   $64.60   $64.60   $64.60  
  Purchase #5 $179.83   3.794%   $186.6528   $186.65   $186.65   $186.70  
  Purchase #6 $198.89   6.550%   $211.9173   $211.92   $211.90   $211.90  
  Purchase #7 $214.74   7.722%   $231.3222   $231.32   $231.30   $231.30  
  7 purchase totals = $1,118.89       $1,202.3771   $1,202.38   $1,202.35   $1,202.40