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 $148.29   8.261%   $160.5402   $160.54   $160.55   $160.50  
  Purchase #2 $182.43   11.530%   $203.4642   $203.46   $203.45   $203.50  
  Purchase #3 $35.29   9.864%   $38.771   $38.77   $38.75   $38.80  
  Purchase #4 $98.31   9.120%   $107.2759   $107.28   $107.30   $107.30  
  Purchase #5 $82.79   4.456%   $86.4791   $86.48   $86.50   $86.50  
  Purchase #6 $80.95   5.265%   $85.212   $85.21   $85.20   $85.20  
  Purchase #7 $89.30   7.169%   $95.7019   $95.70   $95.70   $95.70  
  7 purchase totals = $717.36       $777.4443   $777.44   $777.45   $777.50