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 $54.49   12.701%   $61.4108   $61.41   $61.40   $61.40  
  Purchase #2 $173.57   4.147%   $180.7679   $180.77   $180.75   $180.80  
  Purchase #3 $219.50   9.841%   $241.101   $241.10   $241.10   $241.10  
  Purchase #4 $87.87   11.392%   $97.8802   $97.88   $97.90   $97.90  
  Purchase #5 $74.75   3.324%   $77.2347   $77.23   $77.25   $77.20  
  Purchase #6 $168.54   5.380%   $177.6075   $177.61   $177.60   $177.60  
  Purchase #7 $214.49   4.150%   $223.3913   $223.39   $223.40   $223.40  
  7 purchase totals = $993.21       $1,059.3934   $1,059.39   $1,059.40   $1,059.40