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 $191.37   7.356%   $205.4472   $205.45   $205.45   $205.40  
  Purchase #2 $250.77   10.835%   $277.9409   $277.94   $277.95   $277.90  
  Purchase #3 $132.79   8.809%   $144.4875   $144.49   $144.50   $144.50  
  Purchase #4 $214.86   13.539%   $243.9499   $243.95   $243.95   $243.90  
  Purchase #5 $245.84   7.177%   $263.4839   $263.48   $263.50   $263.50  
  Purchase #6 $151.58   3.496%   $156.8792   $156.88   $156.90   $156.90  
  Purchase #7 $9.72   3.475%   $10.0578   $10.06   $10.05   $10.10  
  7 purchase totals = $1,196.93       $1,302.2464   $1,302.25   $1,302.30   $1,302.20