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 $238.44   10.743%   $264.0556   $264.06   $264.05   $264.10  
  Purchase #2 $44.86   8.600%   $48.718   $48.72   $48.70   $48.70  
  Purchase #3 $246.50   10.450%   $272.2593   $272.26   $272.25   $272.30  
  Purchase #4 $174.57   6.821%   $186.4774   $186.48   $186.50   $186.50  
  Purchase #5 $53.83   11.435%   $59.9855   $59.99   $60.00   $60.00  
  Purchase #6 $178.42   6.730%   $190.4277   $190.43   $190.45   $190.40  
  Purchase #7 $11.70   11.447%   $13.0393   $13.04   $13.05   $13.00  
  7 purchase totals = $948.32       $1,034.9628   $1,034.98   $1,035.00   $1,035.00