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 $165.53   12.833%   $186.7725   $186.77   $186.75   $186.80  
  Purchase #2 $211.35   6.561%   $225.2167   $225.22   $225.20   $225.20  
  Purchase #3 $169.34   13.615%   $192.3956   $192.40   $192.40   $192.40  
  Purchase #4 $33.78   9.247%   $36.9036   $36.90   $36.90   $36.90  
  Purchase #5 $202.53   8.671%   $220.0914   $220.09   $220.10   $220.10  
  Purchase #6 $249.70   4.299%   $260.4346   $260.43   $260.45   $260.40  
  Purchase #7 $232.76   9.127%   $254.004   $254.00   $254.00   $254.00  
  7 purchase totals = $1,264.99       $1,375.8184   $1,375.81   $1,375.80   $1,375.80