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 $152.77   12.849%   $172.3994   $172.40   $172.40   $172.40  
  Purchase #2 $180.38   13.573%   $204.863   $204.86   $204.85   $204.90  
  Purchase #3 $126.32   7.705%   $136.053   $136.05   $136.05   $136.10  
  Purchase #4 $153.55   6.111%   $162.9334   $162.93   $162.95   $162.90  
  Purchase #5 $250.32   13.500%   $284.1132   $284.11   $284.10   $284.10  
  Purchase #6 $247.91   4.841%   $259.9113   $259.91   $259.90   $259.90  
  Purchase #7 $141.26   7.586%   $151.976   $151.98   $152.00   $152.00  
  7 purchase totals = $1,252.51       $1,372.2493   $1,372.24   $1,372.25   $1,372.30