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 $94.61   8.380%   $102.5383   $102.54   $102.55   $102.50  
  Purchase #2 $52.67   5.862%   $55.7575   $55.76   $55.75   $55.80  
  Purchase #3 $124.58   10.351%   $137.4753   $137.48   $137.50   $137.50  
  Purchase #4 $162.59   7.818%   $175.3013   $175.30   $175.30   $175.30  
  Purchase #5 $176.64   3.627%   $183.0467   $183.05   $183.05   $183.00  
  Purchase #6 $130.36   3.714%   $135.2016   $135.20   $135.20   $135.20  
  Purchase #7 $184.80   11.450%   $205.9596   $205.96   $205.95   $206.00  
  7 purchase totals = $926.25       $995.2803   $995.29   $995.30   $995.30