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 $144.75   7.804%   $156.0463   $156.05   $156.05   $156.00  
  Purchase #2 $82.63   12.126%   $92.6497   $92.65   $92.65   $92.60  
  Purchase #3 $161.25   12.349%   $181.1628   $181.16   $181.15   $181.20  
  Purchase #4 $174.86   9.603%   $191.6518   $191.65   $191.65   $191.70  
  Purchase #5 $248.44   13.107%   $281.003   $281.00   $281.00   $281.00  
  Purchase #6 $145.79   10.773%   $161.496   $161.50   $161.50   $161.50  
  Purchase #7 $238.59   6.280%   $253.5735   $253.57   $253.55   $253.60  
  7 purchase totals = $1,196.31       $1,317.5831   $1,317.58   $1,317.55   $1,317.60