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 $39.38   8.566%   $42.7533   $42.75   $42.75   $42.80  
  Purchase #2 $58.74   3.573%   $60.8388   $60.84   $60.85   $60.80  
  Purchase #3 $155.51   5.187%   $163.5763   $163.58   $163.60   $163.60  
  Purchase #4 $214.29   5.640%   $226.376   $226.38   $226.40   $226.40  
  Purchase #5 $100.61   12.738%   $113.4257   $113.43   $113.45   $113.40  
  Purchase #6 $197.42   10.652%   $218.4492   $218.45   $218.45   $218.40  
  Purchase #7 $190.88   8.605%   $207.3052   $207.31   $207.30   $207.30  
  7 purchase totals = $956.83       $1,032.7245   $1,032.74   $1,032.80   $1,032.70