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 $57.57   13.534%   $65.3615   $65.36   $65.35   $65.40  
  Purchase #2 $23.48   11.825%   $26.2565   $26.26   $26.25   $26.30  
  Purchase #3 $200.55   6.713%   $214.0129   $214.01   $214.00   $214.00  
  Purchase #4 $89.44   8.200%   $96.7741   $96.77   $96.75   $96.80  
  Purchase #5 $180.51   11.318%   $200.9401   $200.94   $200.95   $200.90  
  Purchase #6 $197.26   11.486%   $219.9173   $219.92   $219.90   $219.90  
  Purchase #7 $209.26   7.804%   $225.5907   $225.59   $225.60   $225.60  
  7 purchase totals = $958.07       $1,048.8531   $1,048.85   $1,048.80   $1,048.90