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 $61.40   6.204%   $65.2093   $65.21   $65.20   $65.20  
  Purchase #2 $211.88   13.654%   $240.8101   $240.81   $240.80   $240.80  
  Purchase #3 $63.40   12.168%   $71.1145   $71.11   $71.10   $71.10  
  Purchase #4 $97.79   9.400%   $106.9823   $106.98   $107.00   $107.00  
  Purchase #5 $194.70   3.232%   $200.9927   $200.99   $201.00   $201.00  
  Purchase #6 $108.79   4.550%   $113.7399   $113.74   $113.75   $113.70  
  Purchase #7 $196.53   6.141%   $208.5989   $208.60   $208.60   $208.60  
  7 purchase totals = $934.49       $1,007.4477   $1,007.44   $1,007.45   $1,007.40