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 $60.48   8.699%   $65.7412   $65.74   $65.75   $65.70  
  Purchase #2 $240.38   5.866%   $254.4807   $254.48   $254.50   $254.50  
  Purchase #3 $192.52   5.860%   $203.8017   $203.80   $203.80   $203.80  
  Purchase #4 $14.80   5.798%   $15.6581   $15.66   $15.65   $15.70  
  Purchase #5 $215.67   11.712%   $240.9293   $240.93   $240.95   $240.90  
  Purchase #6 $190.52   12.173%   $213.712   $213.71   $213.70   $213.70  
  Purchase #7 $235.37   13.339%   $266.766   $266.77   $266.75   $266.80  
  7 purchase totals = $1,149.74       $1,261.0890   $1,261.09   $1,261.10   $1,261.10