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 $171.91   4.751%   $180.0774   $180.08   $180.10   $180.10  
  Purchase #2 $193.90   4.748%   $203.1064   $203.11   $203.10   $203.10  
  Purchase #3 $192.77   5.306%   $202.9984   $203.00   $203.00   $203.00  
  Purchase #4 $173.77   10.650%   $192.2765   $192.28   $192.30   $192.30  
  Purchase #5 $162.42   5.523%   $171.3905   $171.39   $171.40   $171.40  
  Purchase #6 $213.29   13.502%   $242.0884   $242.09   $242.10   $242.10  
  Purchase #7 $190.43   12.795%   $214.7955   $214.80   $214.80   $214.80  
  7 purchase totals = $1,298.49       $1,406.7331   $1,406.75   $1,406.80   $1,406.80