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 $69.84   11.576%   $77.9247   $77.92   $77.90   $77.90  
  Purchase #2 $163.42   13.601%   $185.6468   $185.65   $185.65   $185.60  
  Purchase #3 $246.72   12.776%   $278.2409   $278.24   $278.25   $278.20  
  Purchase #4 $203.98   8.458%   $221.2326   $221.23   $221.25   $221.20  
  Purchase #5 $53.38   9.779%   $58.6   $58.60   $58.60   $58.60  
  Purchase #6 $187.62   7.106%   $200.9523   $200.95   $200.95   $201.00  
  Purchase #7 $173.45   4.259%   $180.8372   $180.84   $180.85   $180.80  
  7 purchase totals = $1,098.41       $1,203.4345   $1,203.43   $1,203.45   $1,203.30