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 $240.84   10.283%   $265.6056   $265.61   $265.60   $265.60  
  Purchase #2 $155.32   4.291%   $161.9848   $161.98   $162.00   $162.00  
  Purchase #3 $66.51   13.252%   $75.3239   $75.32   $75.30   $75.30  
  Purchase #4 $127.25   7.698%   $137.0457   $137.05   $137.05   $137.00  
  Purchase #5 $61.41   6.833%   $65.6061   $65.61   $65.60   $65.60  
  Purchase #6 $87.55   8.336%   $94.8482   $94.85   $94.85   $94.80  
  Purchase #7 $217.86   3.489%   $225.4611   $225.46   $225.45   $225.50  
  7 purchase totals = $956.74       $1,025.8754   $1,025.88   $1,025.85   $1,025.80