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 $86.48   10.846%   $95.8596   $95.86   $95.85   $95.90  
  Purchase #2 $114.93   13.395%   $130.3249   $130.32   $130.30   $130.30  
  Purchase #3 $143.38   11.322%   $159.6135   $159.61   $159.60   $159.60  
  Purchase #4 $239.78   10.803%   $265.6834   $265.68   $265.70   $265.70  
  Purchase #5 $185.28   8.507%   $201.0418   $201.04   $201.05   $201.00  
  Purchase #6 $77.89   13.361%   $88.2969   $88.30   $88.30   $88.30  
  Purchase #7 $191.26   13.282%   $216.6632   $216.66   $216.65   $216.70  
  7 purchase totals = $1,039.00       $1,157.4833   $1,157.47   $1,157.45   $1,157.50