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 $196.35   9.827%   $215.6453   $215.65   $215.65   $215.60  
  Purchase #2 $93.83   13.319%   $106.3272   $106.33   $106.35   $106.30  
  Purchase #3 $34.43   7.367%   $36.9665   $36.97   $36.95   $37.00  
  Purchase #4 $22.84   7.746%   $24.6092   $24.61   $24.60   $24.60  
  Purchase #5 $228.34   13.428%   $259.0015   $259.00   $259.00   $259.00  
  Purchase #6 $70.42   3.347%   $72.777   $72.78   $72.80   $72.80  
  Purchase #7 $129.40   11.364%   $144.105   $144.11   $144.10   $144.10  
  7 purchase totals = $775.61       $859.4317   $859.45   $859.45   $859.40