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 $113.34   3.627%   $117.4508   $117.45   $117.45   $117.50  
  Purchase #2 $248.57   11.747%   $277.7695   $277.77   $277.75   $277.80  
  Purchase #3 $74.57   10.851%   $82.6616   $82.66   $82.65   $82.70  
  Purchase #4 $181.84   13.322%   $206.0647   $206.06   $206.05   $206.10  
  Purchase #5 $100.74   5.864%   $106.6474   $106.65   $106.65   $106.60  
  Purchase #6 $169.48   12.561%   $190.7684   $190.77   $190.75   $190.80  
  Purchase #7 $19.41   4.826%   $20.3467   $20.35   $20.35   $20.30  
  7 purchase totals = $907.95       $1,001.7091   $1,001.71   $1,001.65   $1,001.80