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 $39.81   10.528%   $44.0012   $44.00   $44.00   $44.00  
  Purchase #2 $131.54   11.768%   $147.0196   $147.02   $147.00   $147.00  
  Purchase #3 $44.67   6.265%   $47.4686   $47.47   $47.45   $47.50  
  Purchase #4 $226.57   5.656%   $239.3848   $239.38   $239.40   $239.40  
  Purchase #5 $148.67   12.590%   $167.3876   $167.39   $167.40   $167.40  
  Purchase #6 $99.82   13.565%   $113.3606   $113.36   $113.35   $113.40  
  Purchase #7 $104.60   3.546%   $108.3091   $108.31   $108.30   $108.30  
  7 purchase totals = $795.68       $866.9315   $866.93   $866.90   $867.00